JP4391664B2 - Ground improvement structure and construction method for soft ground - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground improvement method for improving hard ground by discharging water contained in soft ground.
[0002]
[Prior art]
A vacuum consolidation method is known as a method for improving soft and viscous ground such as landfill layer, sludge layer and peat layer. In such a vacuum consolidation method, a plurality of drain materials are placed on the ground to be improved, the upper ends are extended to the ground, and water-permeable materials such as sand mats and drain materials are laid to contact the upper ends of the drain materials. A perforated pipe is placed under the material and a pump is connected to it, and an airtight sheet material is applied to the entire area of the ground to be improved so as to cover the drain material upper end, the water flow material and the perforated pipe in an airtight manner. Lay down. Then, by operating the pump, a vacuum pressure acts on the ground covered with the sheet material, and this vacuum pressure is transmitted from the perforated pipe to the drain material through the water-permeable material and further transmitted into the ground. When the vacuum pressure acts in the ground in this way, the water in the ground is sucked by the vacuum pressure, flows from the drain material to the perforated tube through the water flow material, and is discharged to the ground.
[0003]
[Problems to be solved by the invention]
However, the conventional vacuum consolidation method has the following problems.
(1) In order to promote drainage from the drain material, it is necessary to lay a sheet material in the entire area of the ground to be improved, and the material cost of the sheet material is high, and the labor of laying work is complicated.
(2) Even when the vacuum consolidation method is used in combination with road embankment, since the entire improved area is covered with an airtight sheet and embankment is performed on it, there are problems in terms of construction cost and construction period.
(3) In order to maintain a wide range of the ground surface covered with the sheet material in an airtight manner, the labor during the construction period is complicated.
[0004]
The present invention focuses on the above-mentioned problems of the prior art and solves this problem. The problem is that the moisture in the ground to be improved can be efficiently removed by simply covering a limited area with a sheet material. An object of the present invention is to provide a ground improvement structure and method capable of draining.
[0005]
In order to solve the above problems, the present invention, soil improvement target area consists of a pumping zone and drainage zone, the drainage area, covered with water-impermeable material, such as mud upper end sealed from the outside air and ground surface water We, the lower end is provided with a plurality of drain material so as to reach the aquifer improved target ground below, wherein the pumping area disposed in the drainage zone, the lower end extends the upper end until the improvements subject soil improvement target ground lower permeability A plurality of drain materials are provided so as to reach the layer, and a water-permeable material for guiding water from the upper end of the drain material to a predetermined position is laid so as to contact the upper end of the drain material, and the water-permeable material is perforated. by intersecting the tube was placed, by the water passage material and the perforated tube and the plurality of drain material was coated in an airtight sheet material, provided with a pump in communication with the organic hole tube, with the pump Through the water-permeable material and the perforated pipe Soil Improvement structure of soft ground which enables consolidation target ground by sucking water from the water zone to the drain zone in the drain member is provided.
[0006]
In the ground improvement structure of the present invention, with this configuration, the water in the ground falls through the drain material to the permeable layer below the improvement target ground in the drainage area, while the water in the permeable layer passes through the drain material in the pumped area. Rise.
In other words, the drain material in the drainage area is installed so that the upper end does not communicate with the outside air and the lower end reaches the water permeable layer below the ground to be improved. Only water permeates and flows down to the permeable layer. On the other hand, the drainage material in the pumping area is provided so that the water-permeable material and the perforated pipe communicate with each other at the upper end protruding above the ground, and is airtightly covered with the sheet. The suction force from the pump on the ground acts to the permeable layer, and the water in the permeable layer and the ground penetrates from the lower end of the drain material and is sucked up to the ground. Therefore, if only the pumping area is covered with the sheet, a good compaction effect can be obtained in the entire area of the ground improvement target area including this pumping area, so the material cost of the sheet material is reduced and the laying work becomes much easier. Become.
[0007]
In the ground improvement structure of the present invention, the arrangement relationship between the pumping area and the drainage area is not particularly limited as long as drainage from the ground can be efficiently performed. The pumping areas can be arranged so as to surround, or the pumping areas can be arranged to be scattered in the drainage area. The pump may be installed either in the pumping area or drainage area of the ground improvement target area or outside the ground improvement target area as long as it can communicate with the water-permeable material and the perforated pipe.
[0008]
In the ground improvement structure of the present invention, the upper end of the drain material stays in the ground to be improved or is covered with the water-impermeable material so as not to communicate with the outside air. If the soil is made of clay, refill the top of the drain hole, or if the surface of the ground to be improved consists of sand mats, drop the top of the drain material into the drain hole and backfill with impervious viscous soil. For example, the upper end of the drain material does not communicate with the outside air, and the surface water can be prevented from penetrating into the drain material.
[0009]
In the present invention, a boundary region between the improvement target ground and the non-improvement target ground is provided with a water-impervious wall that penetrates the water permeable layer to block the flow of groundwater from the non-improvement target ground, It is preferable to minimize settlement.
[0012]
In the present invention, the drain material guides the moisture contained in the ground of the drainage area to the lower permeable layer, or the moisture contained in the permeable layer of the pumped area and the ground to the upper permeable material and the perforated pipe. Any material can be used as long as it can be guided, for example, a cardboard drain material, a sand drain, and a flexible pipe drain material that can be expanded and contracted in a cylindrical shape can be used. The flexible pipe drain material is relatively easy to handle and place and is excellent in economic efficiency. In particular, the flexible pipe drain material is optimal because it has an excellent water collecting effect.
In addition, as the flexible pipe drain material, for example, a synthetic resin bone member formed in a spiral shape and a fibrous filter attached to the bone member is configured to be a stretchable and bendable cylindrical shape. Can be used, and this is often used as a drain for preventing liquefaction of the ground.
[0013]
In the present invention, a pumping area and a drainage area are set in the ground improvement target area, and in the drainage area, a plurality of drain materials are arranged at the upper end so that the outside air and the ground surface water are not communicated with an impermeable material . lower is extended up to aquifer improved target ground below, in the drainage zone pumping area was placed in, and extends a plurality of drain material from aquifer improved target ground down to the improved target ground, said plurality of communicated to the pumping zone outside of the pump through the water passage material and perforated pipe in the drain member, said plurality of drain material upper, the water passage material and the perforated tube covered hermetically by a sheet material, said pump From the drainage layer through the drainage material in the pumped area to the pump through the water-permeable material and the perforated pipe to drain the water, and through the drain material in the drainage area The ground improvement construction method of the soft ground which makes the said improvement object ground compact by guiding the water of this to the said permeable layer is provided.
[0015]
In the ground improvement method of the present invention, when using a cardboard drain material as a drain material in the drainage area, a jig with a blade attached to the tip of the shaft material is inserted into the hole after the drain material is placed and cut. Then, the upper end of the drain material can be installed several meters lower than the ground surface. Here, as another cutting jig, an apparatus using a high-pressure jet, a hydraulic cylinder, underwater gas cutting, discharge, heat rays, and a disk saw can be used.
In addition, when the drain material in the drainage area is a flexible pipe drain material, if the upper end of the drain material is cut after pulling, the extended drain material contracts and the upper end is installed below the ground surface. can do. It is preferable to attach a lid for preventing inflow of earth and sand into the cylinder at the upper end of the flexible pipe drain material.
As another method, after cutting the drain material near the ground surface, the upper end of the drain material is hooked to a jig provided with a hook at the tip of the shaft member, to a predetermined depth in the drain hole. It may be pushed down, and at this time, a high-pressure jet can be used in combination.
On the other hand, when using a sand drain as a drain material, the top of the drain material can be formed to be several meters below the ground surface by adjusting the amount of sand thrown into the hole. Backfill with soil.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although an example is described based on an accompanying drawing, the present invention is not limited to this.
FIG. 1 is a sectional view showing a ground improvement structure according to the present invention, and FIGS. 2A and 2B are a sectional view and a plan view, respectively, of a pumping area. 1 and 2, the ground improvement structure 10 includes a drainage area 20 and a pumping area 21. In the drainage area 20, a plurality of drainage drain materials 15 are placed in the improvement target ground, while in the pumping area 21. A plurality of pumped drain materials 16 are laid in the ground to be improved, and a perforated pipe 12b and a plurality of water-permeable materials 12a are laid on the ground surface. The sheet material 11 is laid on the ground surface so that the tube 12b is hermetically covered, a vacuum pump 17 is provided so as to communicate with the perforated tube 12b through the connecting tube 18, and a water shielding wall (not shown) Is provided in the boundary area between the improvement target ground 13 and the non-improvement target ground.
In addition, in a present Example, although the case where there is only one permeable layer below the improvement target ground is described, the present invention can also be applied to a ground having many permeable layers.
[0017]
The drainage drain material 15 in the drainage area 20 reaches the water permeable layer 14 below the ground to be improved and stays in the ground 13 to be improved so that the upper end does not communicate with the outside air or the surface water. It is backfilled with mud 24 as a material, and is arranged at intervals of about 1 to 2 m.
On the other hand, the pumping drain material 16 in the pumping area 21 is provided such that the lower end reaches the water permeable layer 14 below the improvement target ground, and the upper end 16a protrudes from the ground surface of the improvement target ground 13 at intervals of about 1 m. Be placed.
[0018]
Here, as the drainage drain material 15 and the pumped drain material 16, for example, a cardboard drain material, a sand drain, a flexible pipe drain material formed in a cylindrical shape, and the like can be used. In consideration of ease, economy, and water collection effect, a cylindrical pipe material that can be stretched and bent is particularly suitable.
[0019]
The water-permeable material 12a is formed in a band shape, and is laid at predetermined intervals so as to come into contact with the upper end 16a of the drainage drain material protruding from the ground surface as shown in FIGS. 2 (a) and 2 (b). . The perforated pipe 12b is a pipe body such as a vinyl chloride pipe that has a plurality of holes, and extends so as to intersect the plurality of water-permeable materials 12a. In FIGS. 2A and 2B, the water-permeable material 12a is illustrated as being positioned on the perforated pipe 12b. However, the upper and lower positional relationship can be reversed. Further, the sheet material 11 has both end portions 11a embedded in the improvement target ground 13 so that outside air does not flow into the inside from the both end portions 11a.
[0020]
Moreover, the impermeable wall provided in the boundary area | region of the said improvement object ground 13 and the non-improvement object ground can be formed with a soil mortar, a steel sheet pile, or fluidized mud.
For example, in a ground where the permeable layer has a large expanse compared to the target area for ground improvement, if ground improvement is performed without providing a water-impervious wall, groundwater will be collected from the non-improvement target ground. In the target ground, the consolidation effect is reduced, while in the non-improved target ground, ground subsidence may occur.
Therefore, if the impermeable wall that penetrates the water permeable layer is constructed in the boundary area between the improvement target ground 13 and the non-improvement target ground, groundwater collection from the non-improvement target ground is prevented, so the above problem is solved. Is done.
[0021]
Although not shown, the pumping area 21 may be provided with a pumping device, a so-called well point system, in which a well point is connected to the tip of a pipe and a vacuum pump is connected to the pipe via a pipe. . The well point system has an outer diameter of 5 to 6 cm and a length of about 1 m of a pipe body and a water absorption pipe having a hole formed in the axial direction, that is, a well point and a well point connected to the well point. A plurality of pumping pipes having a length of about 4 to 6 m arranged at predetermined intervals in the vertical direction, a header pipe connected to the upper ends of the plurality of pumping pipes and extending to the ground, and a vacuum connected to the header pipe A vacuum pump, a separation device that separates discharged water and air, and an exhaust device and a drain device that perform exhaust and drainage through the separation device, respectively.
[0022]
Next, FIG. 3 is a plan view showing the positional relationship between the drainage area 20 and the pumping area 21 in FIG. 1. Here, the pumping area 21 is arranged so as to surround the drainage area 20. 4 differs from FIG. 3 in that the pumping areas 21 are arranged so as to be scattered in the drainage area 20. In other words, the arrangement relationship between the drainage area 20 and the pumping area 21 is within a range where drainage from the ground can be efficiently performed in consideration of the ground conditions, the shape of the target area for ground improvement, the suction capacity of the vacuum pump 17, and the like. Can be changed as appropriate. For example, when the present invention is applied to road embankment, a belt-shaped pumping area 21 may be disposed along the embankment skirt (see FIG. 1).
[0023]
FIG. 5 is a simplified diagram for explaining the ground improvement method according to the present invention, and shows only a part of the steps. Hereinafter, the ground improvement method will be described with reference to FIG.
First, in order to improve workability, the sand mat 25 is formed by sanding the improvement target ground 13. Next, the drain placing machine 30 is run on the sand mat 25 to place the drainage drain material 15 and the pumped drain material 16 at predetermined intervals.
At this time, the drainage drain material 15 is driven so that the lower end reaches the water permeable layer 14 and the upper end remains in the ground about 1 to 2 m below the ground surface, while the pumped drain material 16 is not shown in FIG. However, the lower end reaches the water permeable layer 14 and the upper end protrudes to the ground surface.
[0024]
More specifically, the drainage drain material 15 and the pumping drain material 16 are cast with their upper ends extended to the ground surface, and the upper end 16a of the pumping drain material 16 is bent to the ground surface as it is, while the upper end of the drainage drain material 15 is placed. 15a extends to the ground surface and is driven, and an operator 26 pushes the upper end 15a to about 1 to 2 m underground with a pushing jig 27, and a mud pump 31 drives the mud 24 into the hole. Thereby, the upper end of the drainage drain material 15 can be sealed from the atmosphere and surface water. In addition, instead of the mud 24, a shell-type lid made of foamed polystyrene may be inserted in the hole. Further, in the case of using the embankment 22 as a loading load or in the case of road embankment, the embedding material is disposed in the drainage area 20 to replace the airtightness of the drainage drain material upper end 15a with the embankment material (cohesive soil). be able to.
[0025]
Although not shown, as a method for treating the drainage drain material other than the above, the drainage drainage material 15 is placed so that the upper end 15a of the drainage drainage material 15 remains at a depth of about 1 to 2 m below the entire area of the ground 13 to be improved. Then, an impervious layer with a thickness of about 1 to 2 m is formed by stirring and spreading the viscous soil layer on the drainage drain material, thereby sealing the upper end of the drainage drain material 15 from the atmosphere and surface water. You may do it.
[0026]
Moreover, the construction in the pumping area 21 where the pumping of the drainage drain material 16 has been completed is further advanced before or after the drainage drain material driving process. That is, as shown in FIG. 2 (b), in the pumping area 21, the perforated pipe 12b extends between the pumped drain material upper ends 16a and comes into contact with the pumped drain material upper end 16a from above the perforated pipes 12b. Thus, the belt-shaped water-permeable material 12a is laid at a predetermined interval. Then, the vacuum pump 17 is connected to the perforated pipe 12b through the connecting pipe 18, and the pumped drain material upper end 16a, the water flow material 12a and the perforated pipe 12b are covered with the sheet material 11, and both ends of the sheet material 11 are covered. 11a is buried in the ground.
[0027]
The effect | action in the ground improvement structure 10 formed as mentioned above is demonstrated. When the vacuum pump 17 is operated, air is exhausted from the inside covered with the sheet material 11 and a vacuum pressure acts on the air, and this vacuum pressure is applied from the connecting pipe 18 to the water flow material 12a through the perforated pipe 12b. Furthermore, the vacuum pressure is transmitted from the water flow material 12a to the pumped drain material 16. Thereby, the water in the water permeable layer 14 is sucked upward through the pumped drain material 16 and the water contained in the improvement target ground 13 is also sucked up to the ground through the pumped drain material 16. Therefore, consolidation settlement proceeds and the pumped area 21 is improved.
[0028]
On the other hand, the vacuum pressure transmitted from the pumped drain material 16 to the permeable layer 14 further acts on the improvement target ground 13 in the drainage area 20 via the drainage drain material 15. Therefore, the water contained in the improvement target ground 13 is absorbed by the drainage drain material 15 and falls downward to reach the water permeable layer 14, whereby the improvement target ground 13 is consolidated and the ground strength is increased.
That is, on the improvement target ground 13, a pressure of 50 to 80 kN acts as an isotropic consolidation load due to a difference from the atmospheric pressure, the consolidation is promoted, the ground strength is increased, and the residual settlement is suppressed.
[0029]
FIGS. 6A to 6C are diagrams schematically showing an example in which the ground improvement method according to the present invention is applied to a water area such as a coast.
When reclaiming a water area such as a coast, a revetment wall 43 is first constructed, sand is dropped from a sand blasting ship 42 to form a sand mat 45 of about 1 m on the ground 46 below the surface of the water, and this is used as a permeable layer. Next, a pipe 41 for pumping the landfill is floated on the sea 40, and landfill such as clay or soft soil is dropped on the sand mat 45 from the pipe 41, and the landfill 44 is To construct.
In order to improve airtightness, the sand mat 45 is not formed outside the range of ground improvement, and landfill is performed so that surface water remains on the landfill ground 44.
[0030]
Next, the landfill ground 44 is divided into a drainage area and a pumping area.
Then, the drain placing machine 49 mounted on the trolley is floated on the surface water 54, and thereby the drainage drain material 48 is placed in the drainage area of the landfill ground 44. At this time, the drainage drain material 48 reaches at least the sand mat 45 at the lower end and cuts the upper end on the landfill ground 44. After the drainage drain material 48 is placed, a water-impermeable layer 47 is formed by spreading a water-impermeable material such as viscous soil to a thickness of about 1 to 2 m.
[0031]
On the other hand, in the pumped area of the landfill 44, after forming the impermeable layer 47, the pumped drain material is driven by the drain driving machine 49. At this time, the pumped drain material is cut by having the lower end reaching at least the sand mat 45 and extending the upper end over the impermeable layer 47. After placing a plurality of pumping drain materials in this way, the non-woven fabric, the perforated pipe and the sheet material are installed in the pumped area by the same method described with reference to FIG. 5, and the perforated pipe is vacuumed via the connecting pipe. Connect the pump.
After constructing the ground improvement structure as described above, if the groundwater is discharged by operating the vacuum pump, a vacuum pressure is applied to the landfill ground 44 in the same manner as described above, and the ground of the landfill ground 44 due to consolidation settlement. Improvements are possible.
[0032]
【The invention's effect】
In the present invention, a drainage area and a pumping area are set on the improvement target ground, and the drainage material of the drainage area is installed so that the upper end does not communicate with the outside air and the lower end reaches the water permeable layer below the improvement target ground. The drain material is installed so that the lower end reaches the permeable layer below the ground to be improved and the upper end protrudes above the ground, and in the pumping area, the drainage means and the sheet material are transmitted so that the vacuum pressure from the pump is transmitted to the drain material. Since the vacuum pressure from the pump on the ground acts on the permeable layer through the drainage material in the pumped area, the vacuum pressure is improved from the permeable layer through the drainage material in the drainage area. To communicate. Therefore, if the sheet is covered only in the pumping area, a vacuum pressure can be applied to the entire area of the ground improvement target area including this pumping area, and a good consolidation effect can be obtained. The construction cost of the laying work such as the bonding work between the sheets can be remarkably suppressed.
[0033]
Further, in the present invention, the minimum necessary range may be set in the pumping area according to the design conditions, so that the laying of seats and the maintenance of airtightness can be saved, and the construction cost can be reduced and the construction period can be shortened. .
[0034]
Furthermore, in the present invention, since the drain material of the drainage area is installed so that the upper end does not communicate with the outside air and the lower end reaches the water permeable layer below the ground to be improved, the ground surface water and the outside air pass through the drainage drain material. Therefore, the water collection efficiency from the ground to be improved through the drainage drain material and the permeable layer can be increased, and the groundwater level in the ground to be improved can be sufficiently lowered. The need for a separate drainage area is reduced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a ground improvement structure according to the present invention.
2 is an enlarged view of a pumping area in FIG. 1, where (a) is a cross-sectional view and (b) is a plan view.
FIG. 3 is a plan view showing a positional relationship between a pumping area and a draining area in FIG.
FIG. 4 is a diagram showing a positional relationship between a pumping area and a drainage area different from FIG. 3;
FIG. 5 is a simplified diagram for explaining a ground improvement method according to the present invention.
FIGS. 6A to 6C are diagrams schematically showing an example in which the ground improvement method according to the present invention is applied to a water area such as a coast.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Ground improvement structure 11 Sheet material 12a Water flow material 12b Perforated pipe 13 Improvement target ground 14 Water-permeable layer 15 Drainage drain material (drain material)
16 Pumped drain material (drain material)
17 Vacuum pump (pump)
20 Drainage area 21 Pumping area

Claims (4)

The ground improvement target area consists of pumping area and drainage area,
In the drainage area, a plurality of drain materials are provided so that the upper end is covered with a water-impermeable material such as mud that seals from outside air or ground surface water , and the lower end reaches a water permeable layer below the ground to be improved,
Wherein the pumping zone disposed in the drainage zone, a plurality of drain material so that the lower end extends to the upper end on an improved target ground reaching the permeable layer of the improved target ground below a predetermined water from the upper end of the drain member A water-permeable material for guiding to a position is laid so as to contact the upper end of the drain material, and the water-permeable material is arranged by crossing perforated pipes, and the plurality of drain materials, the water-permeable material, and the Cover the hole tube with a sheet material in an airtight manner,
By providing a pump in communication with the perforated pipe, the target ground can be consolidated by sucking up the water from the pumping area to the drainage area with the drain material through the water-permeable material and the perforated pipe. Improved ground structure for soft ground . The ground improvement structure for soft ground according to claim 1, wherein the drain material is a stretchable drain material formed in a cylindrical shape. The ground improvement structure of the soft ground according to claim 1 or 2 , wherein a water-impervious wall penetrating the water permeable layer is provided in a boundary region between the ground improvement target region and the non-target region. Set up a pumping area and a drainage area in the ground improvement area,
In the drainage area, the lower end of the drain material is extended to the water permeable layer below the improvement target ground so that the upper end of the plurality of drain materials does not communicate outside air or ground surface water with the impermeable material ,
In pumping zone disposed in the drainage zone, to extend a plurality of drain material from the water permeable layer of the improved target ground down to the improved target ground, via a water passage material and the perforated pipe to the plurality of drain material the communicated with the pumping area outside of the pump, said plurality of drain material upper, the water passage material and the perforated tube covered hermetically by a sheet material,
Running the pump, said with a drain material in the pumping zone from permeable layer through the water passage material and the perforated tube for draining leading water to the pump, the soil through the drain material in the drainage zone The ground improvement construction method of the soft ground which makes the said improvement object ground compact by guiding the water of this to the said water permeable layer.

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