JPH0786218B2 - Method for promoting consolidation of soft and cohesive soil - Google Patents

Description

[Detailed Description of the Invention] (Field of industrial application) The present invention relates to a ground improvement method adopted as a countermeasure for soft and viscous land such as alluvial cohesive land and coastal landfill ground, and particularly to soft viscous soil due to loading embankment. It is applied to the consolidation promotion method when pre-compacting the ground.

(Prior Art) In recent years, development has been actively carried out in waterfront areas, so-called waterfront areas.

The alluvial cohesive soil ground in such areas is often composed mainly of a soft cohesive soil layer that has not been consolidated or is normally consolidated, and is used as the foundation ground of the structure. Often requires some kind of ground improvement.

Conventionally, various construction methods have been proposed and implemented as countermeasures against such soft and viscous ground, but as a method that is relatively economical and can surely obtain an improvement effect, a preconsolidation method using loading embankments is known. There is.

In this construction method, a compaction load corresponding to the structure load is preliminarily applied to the soft and viscous ground by loading embankment or the like in order to impart sufficient proof stress to the structure foundation. In this case, if the soft layer thickness, that is, the consolidation layer thickness is large, the loading period until the consolidation is completed and the required proof stress is obtained becomes longer.Therefore, a drain material made of a water-permeable material is applied to the ground to accelerate consolidation. The so-called vertical drain method is often used together.

The vertical drain method is sand pile, bag sand pile, gravel pile,
By vertically installing paper cardboard, plastic board, etc. in the soft and viscous land at appropriate intervals, the drainage distance is shortened and consolidation is promoted. At this time, the time t required for consolidation is expressed by the following formula from Terzaghi's one-dimensional consolidation theory, and as shown in FIG. 5, consolidation is promoted by shortening the maximum drainage distance.

Here, H: Maximum drainage distance by vertical drain method Th: Time coefficient Cv: Consolidation coefficient.

(Problems to be Solved by the Invention) However, in the vertical drain method as described above, it is necessary to shorten the drain pitch in order to promote consolidation of the soft and viscous ground, and therefore, an extremely large number of drain materials are required. Since it will be placed, the construction cost is high, and there is a problem that the progress of consolidation is delayed due to the disturbance phenomenon to the original ground and the existing structure is adversely affected.

Further, since the drain material is not planarly continuous, it was necessary to lay a sand mat on the drain material to ensure continuity as a drainage channel.

Furthermore, in order to prevent cutting of the drain material due to consolidation settlement, it is necessary to ensure the continuity of the drain material in the vertical direction, and measures to prevent co-climbing at the time of driving the drain material, etc. There were many problems.

The present invention has been made in view of the above problems, and an object thereof is to promote consolidation of soft ground cohesive ground, and to provide a consolidation promotion method which is economical and has excellent workability. is there.

(Means for Solving the Problems) The structure as means of the present invention for solving the above problems is as follows.
In a construction method for carrying out loading embankment on a soft cohesive ground to improve the soil quality of the soft cohesive ground, a grid-shaped thin groove excavated at an appropriate interval in the soft cohesive ground, and the thin groove A feature is that a drainage groove in a grid shape is formed by drilling with a circular hole drilled at the intersection, and a thin film drain material is closely wound around the wall surface of each section surrounded by the drainage groove in a grid shape. The configuration is

(Operation) According to the above-described method for promoting consolidation, since the drain grooves in a grid shape that are continuous in a plane are formed, the interval between the drain grooves is set to be ▲ √ ▼ times the conventional drain pitch. Also has the same effect of promoting consolidation. Further, the continuity of the drainage groove in the vertical direction can be secured.

Further, by tightly winding the thin film drain material around the wall surface of each compartment, it is possible to protect the groove wall of the drainage groove and prevent clogging, and to ensure the water permeability of the drainage groove.

(Example) Hereinafter, one example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a plan view showing a state in which a drainage channel is filled with a water-permeable material. In this embodiment, first, a soft and viscous landbed n is
The grid-shaped drainage groove 1 as shown in FIG.
Form by excavating in.

As shown in FIG. 2, the thin groove excavator A has a pair of left and right side casings 3 each having a pilot bit 3a at the lower end thereof.
And a pair of left and right disc cutters 5 rotatably supported by the side casing 3, and a reverse bit 4a provided at the middle of the side casing 3 and having a lower end and a reverse pipe 4b for discharging sand and sand. The center casing 4, the pilot bit 3a, the disc cutter 5, and the submersible motor 6 that is a rotational drive source of the reverse bit 4a.

The center casing 4 is the side casing 3
It has almost the same diameter as that of a pair of left and right pilot bits.
The 3a and the disc cutter 5 cancel each other's rotational torque by rotating in the opposite directions.

Using the thin groove excavator A having the above structure, the thin groove 1a and the circular holes 1b and 1c as shown in FIG. 3 are excavated to a predetermined depth in the ground.

At this time, the thin groove 1a is filled with muddy water to protect the groove wall.

By using such a thin excavation note A for thin grooves, excavation work can be easily performed even in a narrow site.

Then, as shown in FIG. 4, a circular hole in the center of the thin groove 1a.
When the thin groove excavator A is rotated by 90 degrees around the center 1c, the thin groove 1a intersecting the circular hole 1c is formed by excavation. In this way, by repeating the above-described excavation in sequence, the thin grooves 1a excavated in a lattice shape and the thin grooves are formed.
The drainage groove 1 is formed by excavation at the intersection of 1a and the circular holes 1b and 1c excavated in the middle.

At this time, the distance a ′ between the drainage grooves 1 is arbitrary by appropriately selecting a combination of the diameter φ of the disk cutter 5 of the thin groove excavator A and the center distance l of the pilot bit 3a and the reverse bit 4a. Can be set to (3rd
Figure).

Therefore, the soil constant of the soft and cohesive ground n (especially the consolidation coefficient Cv
Value) and the interval a ′ of the drainage groove 1 according to the set construction period can be appropriately selected.

The relationship between the distance a ′ of the drainage groove 1 and the maximum drainage distance H ′ in the present invention, and the drain pitch a and the maximum drainage distance H in the conventional vertical drain method are as shown in FIGS. 5 and 6. It becomes as follows (the radius of the drain is not considered).

When a'≈a Therefore, the method of the present invention accelerates the consolidation as compared with the conventional method.

To make H '≒ H Therefore, in order to obtain an equivalent consolidation speed, the drain groove interval a ′ is set to the conventional drain pitch a. It can be long.

Next, the water permeable material 2 is filled in the drainage groove 1 formed by excavation in this way.

The water-permeable material 2 is a natural material or an artificial material having a large water permeability such as sand, gravel, and crushed stone, but it is also possible to appropriately select a conventional drain material.

Then, the drainage ditch 1 thus filled with the water-permeable material 2
Is formed on the soft and viscous ground bed n, and then an embankment having a predetermined thickness is performed (not shown). Due to this embankment, excessive spacing water pressure is generated in the soft and viscous landbed n _{1 of} each section surrounded by the grid-shaped drainage grooves 1, and the pore water in the consolidation layer is drained to the water-permeable material 2 of the drainage grooves 1. As the excess pore water pressure dissipates, consolidation proceeds. FIGS. 7 and 8 show thin groove excavator A as described above.
Then, after excavating the drainage groove 1 in a grid shape consisting of the thin groove 1a and the circular holes 1b and 1c, the thin film drain material is formed on the wall surface of the soft and viscous landbed n ₁ of each section surrounded by the drainage groove 1. 7 is closely wound.

As for the winding method, as shown in FIG. 7, the roll-shaped thin film drain material 7 is inserted into the circular hole 1b or the circular hole 1c,
The circular hole 1b or the circular hole 1c is used as a starting point and wound around the wall surface of each section surrounded by the drainage groove 1.

Then, after the thin film drain material 7 has been wound, the drainage groove 1 is filled with the water permeable material 2.

As the thin film drain material 7, a water permeable sheet such as a commercially available non-woven fabric can be used, and preferably, a sheet-shaped water permeable material having a water passage is used.

As described above, the thin-walled drain material 7 is closely wound around the wall surface of each section of the soft and viscous land n to protect the groove wall of the drainage groove 1 and prevent clogging of the water-permeable material. You can

Therefore, the water permeability and continuity of the drainage groove 1 as a drainage layer can be ensured.

(Effects of the Invention) The present invention has the following effects by having the above-mentioned configuration.

The grid-shaped thin grooves and the circular holes formed at the intersections form a planar drainage layer in a grid pattern, so the maximum drainage distance is shortened compared to the conventional vertical drain method. At the same time, it is possible to promote the dissipation of excess pore water pressure generated in the soft and viscous ground of each section surrounded by the grid-shaped drains.

Further, it is possible to arbitrarily set the interval between the grid-shaped drains in accordance with the soil constant and the construction period.

By wrapping the thin film drain material in close contact with the wall surface of each section surrounded by the grid-shaped drainage groove, it is possible to protect the drainage wall and prevent clogging. Continuity can be secured.

[Brief description of drawings]

1 is a plan view of a drainage ditch, FIG. 2 is a front view of a thin groove excavator, FIG. 3 is a plan view showing one element of an excavation groove formed by the thin groove excavator, and FIG. Is a plan view showing a method of excavating a drainage ditch, FIG. 5 (a) is a sectional view showing the maximum drainage distance in a conventional consolidation method, FIG. 5 (b) is the same plan view, and FIG. A plan view showing the maximum drainage distance in the consolidation promotion method, and FIGS. 7 and 8 are plan views in which a thin film drain material is wound around the wall surface of each section surrounded by a grid-like drainage groove. Also in the figure, 1: Drain groove 1a: Thin groove, 1b, 1c: Circular hole 2: Water permeable material 3: Side casing 3a: Pilot bit 4: Center casing 4a: Reverse bit 5: Disc cutter n: Soft viscous land n ₁ : Indicates the soft and viscous landbed of each section.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masahiro Nakagawa 1-7-1, Kyobashi, Chuo-ku, Tokyo Toda Construction Co., Ltd. (72) Inventor Yuji Tategawa 1-1-7, Kyobashi, Chuo-ku, Tokyo (56) Reference JP-A-1-226913 (JP, A) JP-A-50-21515 (JP, A) JP-A-64-80625 (JP, A)

Claims (1)

[Claims] 1. A method for improving the soil quality of a soft cohesive soil by loading embankment on the soft cohesive soil, in which a grid-shaped thin groove excavated at an appropriate interval in the soft cohesive soil , A circular drain hole is formed by excavating a circular hole at the intersection of the thin grooves, and a thin film drain material is adhered to the wall surface of each section surrounded by the lattice drain groove. A method for promoting consolidation of soft and viscous land, characterized by being wrapped.