JP2007016386A - Construction method for improving soft ground - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a construction method for improving soft ground, which enables an air-impermeable part of a drain material to be formed in a position and a range in a proper depth direction, so that the driving length of the drain material can be changed in such a manner as to flexibly adapt to a change in depth up to a baserock, when the drain material wound up in a reel shape is driven into the soft ground while being paid out. <P>SOLUTION: The air-impermeable part 4 for covering a predetermined length part of an upper end 2a after the drain material 2 is driven is formed by the time the drain material 2 wound up in the reel shape is driven into the soft ground 6 after being paid out. After the drain material 2 is driven, the upper end 2a communicates with a water collecting pipe 16 communicating with a decompression means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a soft ground improvement method in which water in a soft ground flows into the drain material and is drained by inserting a water-permeable drain material into the soft ground and decompressing the space in the drain material. It is.

  Conventionally, as shown in FIG. 8, for each driving length planned for a long drain material 2, a fixed length is not blocked to block ventilation between the space in the drain material 2 and the outside. The air permeable portion 4 is formed in the middle of the drain material 2 and the drain material 2 is wound in a reel shape in advance, and the reel shape is formed in the process of placing the drain material 2 on the soft ground in the field. There has been a soft ground improvement method in which the drain material 2 wound up by the length of the mandrel (not shown) is drawn out by an amount corresponding to the placement length (see, for example, Patent Document 1).

  In the soft ground improvement method disclosed in Patent Document 1, a mandrel (not shown) inserts a draining material 2 corresponding to the placement length into the soft ground, so that the draining material 2 corresponding to the same length is drawn out from the reel shape. Thus, after the mandrel is raised, the drain material 2 is separated between the ground side and the reel side while leaving the air-impermeable portion 4 in the vicinity of the ground surface. Such an operation of placing the drain material 2 is repeatedly performed every time the placement position on the soft ground is moved.

  Moreover, in the soft ground improvement construction method of this patent document 1, the position and range of the depth direction of the air-impermeable part 4 of each drain material 2 laid are as shown in FIG. It was designed to be able to be adjusted to the sum of the upper height and the predetermined depth from the surface.

  Here, in the drain material 2 used in the soft ground improvement method of Patent Document 1 as described above, for example, as shown in FIG. 10, a plurality of ribs 12a forming a plurality of continuous grooves in the length direction are formed. A core material 12 and a water-permeable sheet 14 (corresponding to the water-permeable material) that covers the respective tip portions of the plurality of ribs 12a of the core material 12 to close the groove and form a plurality of spaces inside the drain material 2 are provided. It has a structure.

  In the soft ground improvement method disclosed in Patent Document 1, as shown in FIG. 9, the drainage material 2 and the water collecting pipe 16 that have been placed are communicated with each other via a cap 18 and a drainage hose 20, and then the water collecting pipe 16 is connected. The work of the process of depressurizing the space in the drain material 2 is performed by a decompression means (not shown).

In the process of depressurizing the space in the drain material 2 as described above, a negative pressure seal layer (experienced) that blocks a portion of the viscous soil having a predetermined depth from the ground surface of the soft ground 6 from the ground surface to the ground. And the impervious portion 4 of each drain material 2 is formed at a predetermined depth from the height portion on the ground surface of each drain material 2 and the ground surface. The air was prevented from leaking from the portion (about 1.5 m above), and the airtightness was maintained.
JP 2001-226951 A

  However, in the process of placing the drain material 2 on the soft ground 6, for example, as the placement position moves, the depth to a rock (not shown) below the soft ground 6 may change. In such a case, in order to improve the drainage effect, it is desirable to change the placement length of the drain material 2 in accordance with the change in the depth to the bedrock. In the soft ground improvement method such as Patent Document 1, the position and range in the depth direction of the air-impermeable portion 4 cannot be changed even in such a case, and therefore the placement length of the drain material 2 cannot be changed. There was a problem.

  Therefore, in view of the above-mentioned problems, the present invention flexibly copes with the change in the depth to the rock when the drain material wound in a reel shape is placed on the soft ground while being fed out. An object of the present invention is to provide a soft ground improvement method capable of forming the air-impermeable portion at an appropriate depth position and range so that the installation length can be changed.

In order to solve the above problems, the present invention
A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
Between the time when the drain material wound up in the form of a reel is fed and the time when the drain material is placed in the soft ground, an air-impermeable portion is formed to cover a fixed length portion of the upper end portion after the drain material is placed. And
After the drain material is placed, the upper end portion thereof is communicated with a water collecting pipe communicating with the pressure reducing means.

In order to solve the above problems, the present invention
A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
After placing the drain material, insert the impervious tubular member into the water permeable material from the upper end side of the drain material until the lower end reaches a predetermined underground depth of the soft ground,
Fill the space between this impermeable cylinder member and the water permeable material in the depth range from the upper end side of the drain material to the lower end of the hose,
The upper end portion of the air-impermeable cylinder member is communicated with a water collecting pipe communicating with the pressure reducing means.

In order to solve the above problems, the present invention
A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
After placing the drain material, insert the impervious tubular member into the water permeable material from the upper end side of the drain material until the lower end reaches a predetermined underground depth of the soft ground,
The upper end portion of the drain material is submerged in the soft ground while leaving the upper end portion of the air-impermeable cylindrical member on the ground surface of the soft ground.
The upper end portion of the air-impermeable cylinder member is communicated with a water collecting pipe communicating with the pressure reducing means.

In order to solve the above problems, the present invention
A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
After inserting the drain material, after inserting the impermeable tube member into the soft ground to a certain depth so that the drain material is inserted inside,
The upper end portion of the air-impermeable cylinder member is communicated with a water collecting pipe communicating with the pressure reducing means.

A long drain material having a core material continuous in the length direction and a water-permeable sheet that covers the outer periphery of the cross-section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
The lower end of the drain material is inserted through an impermeable tube member disposed in the mandrel,
While inserting the drain material into the soft ground with the mandrel, the impervious cylindrical member is inserted into the soft ground to a certain depth so that the upper end portion remains on the ground surface,
After pulling up the mandrel and cutting the drain material with a casting length,
The upper end portion of the air-impermeable cylinder member is communicated with a water collecting pipe communicating with the pressure reducing means.

  According to such a soft ground improvement method of the present invention, when the drain material wound up in a reel shape is placed on the soft ground while being drawn out, the drain material is flexibly adapted to the change in depth to the rock. The impervious portion can be formed at a suitable position and range in the depth direction so that the casting length of can be changed.

  Hereinafter, embodiments of the soft ground improvement method according to the present invention will be specifically described with reference to the drawings.

  The soft ground improvement method according to the first embodiment of the present invention will be specifically described below. This embodiment corresponds to claim 1 of the appended claims.

  1 to 3 are diagrams referred to for explaining the soft ground improvement method according to the first embodiment of the present invention. In these drawings, members similar to those used in the soft ground improvement method of Patent Document 1 are described with the same reference numerals, and redundant description of similar configurations is omitted.

  In the soft ground improvement method according to the present embodiment, in the step of placing the drain material 2 on the soft ground 6, as shown in FIG. An impervious portion 4 having a predetermined length is formed by stopping at a predetermined position until the mandrel (not shown) is placed into the soft ground 6 by an amount corresponding to the placement length. .

  For example, as shown in FIG. 2, the air-impermeable portion 4 is formed by winding a synthetic resin film material having airtightness such as a vinyl chloride material around the drain material 2. The rear end of the air-impermeable portion 4 shown in FIG. 1 is a cutting position when the drain material 2 is placed. After forming the air-impermeable portion 4 for the drain material 2 corresponding to the placement length, the drain material 2 is continuously placed in the soft ground 6 with a mandrel (not shown).

  As shown in FIG. 3 (a), the drain material 2 that has been laid has an impervious portion 4 of a certain length at its upper end portion 2a. The airtightness is maintained at a predetermined depth portion. Moreover, since the air-impermeable portion 4 has a certain length, the viscous soil of the soft ground 6 having a depth shallower than the position of the lower end thereof can be used as the negative pressure sealing layer. Yes.

  After the drain material 2 is placed, the upper end portion 2a of the drain material 2 is connected to a water collecting pipe 16 laid after the drain material 2 is placed, as shown in FIG. Then, the space in the drain material 2 is decompressed by a decompression means (not shown) that communicates with the water collecting pipe 16 so that the water in the soft ground 6 flows into the drain material 2 by the vacuum pressure and is drained.

  According to the soft ground improvement method according to the present embodiment as described above, until the drain material 2 corresponding to the driving length is drawn out from the drain material 2 wound up in a reel shape in advance, the soft ground 6 is placed in the soft ground 6. Since the impermeable portion 4 is formed by being stopped at a predetermined position, when the drain material 2 wound up in a reel shape is placed on the soft ground 6 while being fed out, for example, immediately before By referring to the actual placement length of the drain material 2 that has been placed several times in advance, the placement length of the drain material 2 to be placed next can be roughly estimated. The impervious portion 4 can be formed so as to come to an appropriate depth direction position or range of the drain material 2 by changing the placement length of the drain material 2.

  Next, based on FIG. 4, the soft ground improvement construction method which concerns on the 2nd Embodiment of this invention is demonstrated. This embodiment corresponds to claim 2 of the claims.

  In the soft ground improvement method according to the present embodiment, as shown in FIG. 4A, the drain material 2 that is not covered with the air-impermeable portion 4 or the like according to the first embodiment is disposed at its upper end. 2a is placed so as to leave on the ground surface of the soft ground 6.

  Here, although not shown in the drawing, this drain material 2 is one that is driven out by a mandrel (not shown) by drawing out the length of the casting from the long drain material 2 wound up in a reel shape. Further, the core material 12 inside the water permeable sheet 14 in the drain material 2 is not shown in FIG. 4B and later, which will be described later, so as not to complicate the drawing.

  Next, as shown in FIG. 4 (b), a hose 32 is inserted as an impermeable cylinder member into the water permeable sheet 14 from the upper end 2 a side of the drain material 2 that has been placed. Here, the hose 32 inserts the viscous soil of the soft ground 6 having a shallower depth than the lower end portion 32a to a predetermined underground depth that can be used as a negative pressure seal layer. Further, the hose 32 is such that the ventilation between the inside and the outside of the cross section perpendicular to the length direction of the hose 32 is blocked in the length range from the lower end portion 32a to the upper end portion 32b. To. As such a hose 32, the thing made from the thing made from a vinyl or rubber | gum, or the cloth which can interrupt | block ventilation can be used, for example.

  After inserting the hose 32, as shown in FIG. 4C, the viscous soil 34 is poured into the water permeable sheet 14 from the upper end 2 a side of the drain material 2, and the depth range to the lower end 32 a of the hose 32. The space between the hose 32 and the water-permeable sheet 14 is filled with the viscous soil 34, and then the upper end of the hose 32 is placed on the water collecting pipe 16 laid after the drain material 2 is laid as shown in FIG. The part 32b is connected.

  And about all the drain materials 2 laid, after connecting the upper end part 32b of the hose 32 inserted in the water-permeable sheet 14 of this drain material 2 to the nearest water collection pipe 16, it connects to this water collection pipe 16 (not shown) By depressurizing the inside of the drain material 2 by the decompression means, the water in the soft ground 6 flows into the drain material 2 by the vacuum pressure and is drained.

  According to such a soft ground improvement method according to the present embodiment, the clay soil 34 filled in the space between the hose 32 and the water permeable sheet 14 forms an air-impermeable portion. Even if the drain material 2 that has been wound up is placed on the soft ground 6 while being drawn out, the air-impermeable portion of the drain material 2 can be arranged in an appropriate depth direction so that the placement length of the drain material 2 can be changed. It can be formed at a position or range.

  Next, based on FIG. 5, the soft ground improvement construction method which concerns on the 3rd Embodiment of this invention is demonstrated. This embodiment corresponds to claim 3 of the claims.

  In the soft ground improvement method according to the present embodiment, the hose 32 is inserted into the permeable sheet 14 from the upper end portion 2a side of the drainage material 2 that has been laid (see (a of FIG. 5), as in the second embodiment. ) And (b)), as shown in FIG. 5 (c), the upper end 32b of the hose 32 remains on the ground surface, and the pierced thigh with the handle tip formed in a bifurcated shape, not shown. , The upper end 2a of the drain material 2 is bent and submerged in the soft ground 6.

  And as shown in FIG.5 (d), about all the drain materials 2 laid, the upper end part 32b of the hose 32 inserted in the water-permeable sheet 14 of this drain material 2 was connected with the nearest water collection pipe | tube 16. Thereafter, as in the second embodiment, the inside of the drain material 2 is decompressed by a decompression means (not shown) connected to the water collecting pipe 16, so that the water in the soft ground 6 is brought into the drain material 2 by the vacuum pressure. Let it flow and drain.

  According to such a soft ground improvement method according to the present embodiment, the hose 32 forms an air-impermeable portion as it is, so that the drain material 2 wound up in a reel shape is struck against the soft ground 6. Even if it sets, the impermeable part can be formed in the position and range of an appropriate depth direction so that the placement length of the drain material 2 can be changed.

  Next, based on FIG. 6, the soft ground improvement construction method which concerns on the 4th Embodiment of this invention is demonstrated. This embodiment corresponds to claim 4 of the scope of claims.

  In the soft ground improvement method according to the present embodiment, as shown in FIG. 6A, after the drain material 2 is placed in the same manner as in the second embodiment, it is shown in FIG. 6B. As described above, the pipe material 36 is inserted into the soft ground 6 so that the drain material 2 placed therein is inserted as an impermeable cylinder member.

  Here, the pipe material 36 has its upper end portion 36a left on the ground surface, and its lower end portion 36b uses the viscous soil of the soft ground 6 having a shallower depth as a negative pressure sealing layer. Insert to a depth that allows Further, the pipe material 36 is used in which the ventilation between the inside and the outside of the cross section perpendicular to the length direction of the pipe material 36 is blocked in the length range from the upper end portion 36a to the lower end portion 36b. Like that. As such a pipe material 36, the thing made from vinyl chloride, the product made from a vinyl sheet, or rubber | gum can be used.

  After inserting the pipe material 36 into the soft ground 6, as shown in FIG. 6C, a cap 38 is fitted to the upper end portion 36 a of the pipe material 36, and one end portion 40 a of the hose 40 is attached. The pipe 38 is inserted through the cap 38 to allow the pipe 36 and the hose 40 to communicate with each other, and the other end 40 b of the hose 40 is connected to the water collecting pipe 16 as shown in FIG.

  For all the pipe members 36, after connecting the end portion 40b of the hose 40 to the nearest water collecting pipe 16, the decompression means (not shown) that leads to the water collecting pipe 16 as in the second embodiment. By depressurizing the inside of the drain material 2, the water in the soft ground 6 flows into the drain material 2 by the vacuum pressure and is drained.

  According to the soft ground improvement method according to the present embodiment as described above, the pipe material 36 forms an air-impermeable portion, so that the drain material 2 wound up in a reel shape is struck onto the soft ground 6. Even if it sets, the impermeable part can be formed in the position and range of an appropriate depth direction so that the placement length of the drain material 2 can be changed.

  Next, based on FIG. 7, the soft ground improvement construction method which concerns on the 5th Embodiment of this invention is demonstrated. This embodiment corresponds to claim 5 of the claims.

  In the present embodiment, as shown in FIG. 7A, a pipe material 36 is disposed in the mandrel 42 immediately before the drain material 2 is placed, and the pipe material 36 is suspended in the mandrel 42. The lower end of the hanging wire 44 is hooked with a hook or the like, and the height of the soft ground 6 from the ground surface is fixed. Further, the lower end 2 b of the drain material 2 is inserted through the pipe material 36.

  After the preparation so far is completed, the drain material 2 is inserted into the soft ground 6 with the mandrel 42 as shown in FIG. Further, when the drain material 2 is inserted into the soft ground 6, the pipe wire 36 is lowered by loosening the suspension wire 44 and the pipe material 36 leaves its upper end portion 36a on the ground surface. 6 to a certain depth. By inserting the pipe material 36 to a certain depth of the soft ground 6, the viscous soil of the soft ground 6 having a depth shallower than the lower end portion 36b can be used as a negative pressure seal layer.

  Then, as shown in FIG. 7C, the drain material 2 is left in the soft ground 6 and the mandrel 42 is pulled up, and then the drain material 2 is cut off from the placed length portion.

  After such an operation, as in the fourth embodiment, all the pipe members 36 are connected to the nearest through the cap 38 and the hose 40 as shown in FIGS. 7 (d) and 7 (e). After communicating with the water collecting pipe 16, the drainage material 2 is decompressed by a decompression means (not shown) that leads to the water collecting pipe 16, so that the water in the soft ground 6 flows into the draining material 2 by the vacuum pressure and drains. Let

  According to the soft ground improvement method according to the present embodiment as described above, the pipe material 36 forms an air-impermeable portion as in the fourth embodiment. Even if the drain material 2 is fed out on the soft ground 6, the impermeable portion is positioned in an appropriate depth direction and range so that the placement length of the drain material 2 can be changed. Can be formed.

  In the first embodiment, the air-impermeable portion 4 is formed by winding the synthetic resin film material around the drain material 2, but a paint or the like is applied to the outer periphery of the drain material 2. Thus, the air-impermeable portion 4 may be formed.

  Further, in the second to fifth embodiments, the drain material 2 wound in a reel shape is driven while being fed out by the driving length, but it is cut to the driving length from the beginning. Alternatively, the drain material 2 may be placed.

  In the second embodiment, as shown in FIG. 4, the hose 32 is inserted as a gas-impermeable cylindrical member into the water-permeable sheet 14 of the drain material 2. Although not shown, for example, a pipe material or the like having an outer diameter that can be inserted into the water-permeable sheet 14 of the drain material 2 may be inserted. Although not shown, when a pipe material or the like is inserted in the water permeable sheet 14 of the drain material 2 instead of the hose 32, the hose 32 is separated from the upper end portion of the pipe material (not shown). By connecting a hose or the like, the water collecting pipe 16 can be communicated.

It is the schematic which shows the reel-shaped drain material 2 used for the soft ground improvement construction method which concerns on the 1st Embodiment of this invention, and the air-impermeable part 4 formed in the middle of this drain material 2. FIG. It is the cross-sectional schematic of the drain material 2 and the air-impermeable part 4 shown in FIG. It is the schematic which shows the enforcement procedure after placement of the drain material 2 of the soft ground improvement construction method which concerns on the 1st Embodiment of this invention to (a) and (b). It is the schematic which shows the enforcement procedure of the soft ground improvement construction method which concerns on the 2nd Embodiment of this invention from (a) to (d). It is the schematic which shows the enforcement procedure of the soft ground improvement construction method which concerns on the 3rd Embodiment of this invention from (a) to (d). It is the schematic which shows the enforcement procedure of the soft ground improvement construction method which concerns on the 4th Embodiment of this invention from (a) to (d). It is the schematic which shows the enforcement procedure of the soft ground improvement construction method which concerns on the 5th Embodiment of this invention from (a) to (e). It is the schematic which shows the reel-shaped drain material 2 used for the conventional soft ground improvement construction method. It is the schematic which shows the drain material 2, the water collection pipe | tube 16, the cap 18, and the drainage hose 20 which are used for the conventional soft ground improvement construction method. It is the cross-sectional schematic of the drain material 2 shown in FIG.

Explanation of symbols

2 drain material 2a upper end portion 2b lower end portion 4 impermeable portion 6 soft ground 12 core material 12a rib 14 water permeable sheet 16 water collecting pipe 18 cap 20 drain hose 32 hose 32a lower end portion 32b upper end portion 34 viscous soil 36 pipe material 36a upper end portion 36b Lower end 38 Cap 40 Hose 40a, 40b End 42 Mandrel 44 Hanging wire

Claims (5)

A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
Between the time when the drain material wound up in the form of a reel is fed and the time when the drain material is placed in the soft ground, an air-impermeable portion is formed to cover a fixed length portion of the upper end portion after the drain material is placed. And
A soft ground improvement method characterized in that after the drain material is placed, the upper end portion thereof is communicated with a water collecting pipe leading to the pressure reducing means. A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
After placing the drain material, insert the impervious tubular member into the water permeable material from the upper end side of the drain material until the lower end reaches a predetermined underground depth of the soft ground,
Fill the space between this impermeable cylinder member and the water permeable material in the depth range from the upper end side of the drain material to the lower end of the hose,
A soft ground improvement method characterized in that an upper end portion of the air-impermeable tubular member is communicated with a water collecting pipe communicating with the pressure reducing means. A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
After placing the drain material, insert the impervious tubular member into the water permeable material from the upper end side of the drain material until the lower end reaches a predetermined underground depth of the soft ground,
The upper end portion of the drain material is submerged in the soft ground while leaving the upper end portion of the air-impermeable cylindrical member on the ground surface of the soft ground.
A soft ground improvement method characterized in that an upper end portion of the air-impermeable tubular member is communicated with a water collecting pipe communicating with the pressure reducing means. A long drain material having a core material continuous in the length direction and a water-permeable material that covers the outer periphery of the cross section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
After inserting the drain material, after inserting the impermeable tube member into the soft ground to a certain depth so that the drain material is inserted inside,
A soft ground improvement method characterized in that an upper end portion of the air-impermeable tubular member is communicated with a water collecting pipe communicating with the pressure reducing means. A long drain material having a core material continuous in the length direction and a water-permeable sheet that covers the outer periphery of the cross-section of the core material to form a space therein is previously wound in a reel shape, and wound in this reel shape. Pour drain material into the soft ground while paying out the length of the cast material,
In the soft ground improvement construction method of draining the water in the soft ground by flowing into the drain material by depressurizing the space in the drain material by a decompression means,
The lower end of the drain material is inserted through an impermeable tube member disposed in the mandrel,
While inserting the drain material into the soft ground with the mandrel, the impervious cylindrical member is inserted into the soft ground to a certain depth so that the upper end portion remains on the ground surface,
After pulling up the mandrel and cutting the drain material with a casting length,
A soft ground improvement method characterized in that an upper end portion of the air-impermeable tubular member is communicated with a water collecting pipe communicating with the pressure reducing means.

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