JP2013185379A - Vacuum consolidation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum consolidation method capable of applying a negative pressure to weak clay to be disposed for obtaining a sufficient consolidation dewatering effect, and capable of economically performing consolidation dewatering.SOLUTION: An inventive vacuum consolidation method is a vacuum consolidation method for dewatering improvement object soil in a high water content state by vacuum consolidation. The method includes: a step S02 of laying water-impervious sheets on a bottom surface and side faces of a disposal field; a step S03 of forming a sand mat in which drain materials with caps are horizontally embedded on the bottom surface; a step S04 of depositing the improvement object soil in a high water content state on the sand mat; a step S07 of applying a negative pressure to the improvement object soil through the drain materials with caps to perform the vacuum consolidation; a step S08 of excavating the vacuum-consolidated improvement object soil; and a step S10 of cleaning the inside of the drain materials with caps. After the cleaning step, the depositing step and the vacuum consolidation step are repeatedly performed for a new improvement object soil in a high water content state.

Description

  The present invention relates to a vacuum consolidation method using a drained cap material in a horizontal position.

In Hokkaido, etc., there is a clay layer (peat) with a high water content ratio in the surface layer of the ground, and the shear strength of the clay layer (peet) is low, so the use of excavated soil after excavation becomes a problem. Usually, in order to effectively use peat with a high water content, it is carried out by mixing solidified material and sand and using it for embankment material, but when the natural water content of peat becomes as large as 500 to 1000%, Many problems have arisen, such as the amount of solidifying material added being 300 kg / m ³ or more. Therefore, it is desired to dehydrate the clay layer (peat) before the solidification treatment to reduce the amount of the solidification material and the volume after the solidification treatment.

  Regarding the dewatering method of clay, Patent Document 1 discloses a method for treating dredged mud that stores a mud with a flocculant added to dredged mud with a high water content ratio in a treatment yard and dehydrates the dredged mud with a water content of 650% or more. In the middle of sending mud through the sand pipe to the treatment yard, an anionic polymer flocculant is first added to the dredged mud, and then a divalent or trivalent inorganic metal salt aqueous solution is added to the dredged mud. The agglomeration reaction is completed, and the mud soil that has completed the agglomeration reaction is discharged to the treatment yard provided with a drainage mechanism at the bottom through the sand discharge pipe, and is naturally dried and dehydrated (claim 1). ).

  Patent Document 2 discloses a first step of supplying muddy water to the muddy water tank, and a vacuum discharge device that adjusts the inside of the cylindrical filter material provided in the muddy water tank to a negative pressure and discharges filtered water from the filter medium to the outside. A dehydration method comprising: a second step of performing a step, and a third step of bringing the inside of the filter medium from negative pressure to atmospheric pressure or higher when the pressure in the filter medium reaches a desired pressure. (Claim 7 etc.).

JP 2002-316200 A JP 2005-103372 A

  The bottom surface dewatering method of Patent Document 1 has a problem that a sufficient amount of consolidation dewatering cannot be obtained because dehydration of the viscous soil occurs only by the gravity of the clay. Further, Patent Document 2 applies a negative pressure to a wide drain material, adsorbs clay in mud water to the drain material, sends air at atmospheric pressure or higher after consolidation dehydration to the inside of the drain material, The clay adsorbed on the surface of the drain material is peeled off by returning the drain material that has been deformed inward due to the pressure to its original shape. It does not clean and remove clay. Also, the drain material is usually not used economically because it is used only once.

  In view of the problems of the prior art as described above, the present invention can apply negative pressure to soft clay to be disposed of in order to obtain a sufficient consolidation dehydration effect, and can perform consolidation dewatering economically. The object is to provide a vacuum consolidation method.

  In order to achieve the above object, the vacuum consolidation method according to the present embodiment is a vacuum consolidation method in which soil to be improved in a high water content state is dewatered by vacuum consolidation, and a water shielding sheet is laid on the bottom and side surfaces of the disposal site. A step of forming a sand mat in which a drain material with a cap is horizontally embedded on the bottom surface, a step of depositing a soil to be improved in a high moisture content state on the sand mat, and the drain material with a cap A step of performing vacuum consolidation by applying a negative pressure to the soil to be improved, a step of excavating the soil to be improved that has been subjected to the vacuum consolidation, and a step of cleaning the inside of the drained material with a cap with a compression medium. And the deposition step and the vacuum consolidation step are repeatedly performed on the soil to be improved in a new high water content state after the cleaning step.

  According to this vacuum consolidation method, the soil to be improved in a high water content state is deposited on a sand mat in which a drain material with a cap is horizontally embedded, and then negative pressure is applied to the soil to be improved through the drain material with a cap. Since vacuum consolidation is performed, a sufficient consolidation dehydration effect can be obtained. In addition, after the vacuum consolidation, the inside of the drained material with cap is washed with a compression medium, and then the soil to be improved with a new high water content is deposited, and the vacuum consolidation process is repeated in the same manner, so that the drain with cap is performed. Since the material can be used repeatedly, consolidation dehydration can be carried out economically.

  In the vacuum consolidation method, compressed air or pressurized water is used as the compression medium, and the cleaning step is performed by connecting the compressed air device or the pressurized water device to a drain hose connected to the drain material with the cap. Easy to execute.

  By covering the surface of the soil to be improved with an airtight sheet and then performing the vacuum consolidation, the consolidation dewatering effect is further improved.

  According to the vacuum consolidation method of the present invention, a negative pressure can be applied to a soft clay to be disposed to obtain a sufficient consolidation dewatering effect and consolidation dewatering can be carried out economically.

It is sectional drawing which shows roughly the vacuum consolidation system comprised by embedding the drain material with a cap in a disposal site in order to perform the vacuum consolidation method of this embodiment. It is a top view which shows roughly the state which laid the drain material with a cap in the disposal site of FIG. It is a top view which shows the cap part of the plastic board drain with a cap which can be used as a drain material with a cap of FIG. 1, FIG. It is sectional drawing (a) which cut | disconnected the plastic board drain (PBD) of FIG. 3 in the IVA-IVA line direction, and sectional drawing (b) which expanded the part. It is a schematic sectional drawing for demonstrating the washing | cleaning means of PBD13 with a cap in the vacuum compaction system of this embodiment. It is a flowchart for demonstrating process S01-S10 of the vacuum consolidation method of this embodiment. It is a flowchart for demonstrating process S21-S24 for performing washing | cleaning process S10 of FIG. It is sectional drawing which cut | disconnected the disposal site 10 of FIG. 1 in the paper surface perpendicular | vertical direction.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a vacuum consolidation system constructed by embedding a drain material with a cap in a disposal site in order to execute the vacuum consolidation method of the present embodiment. FIG. 2 is a plan view schematically showing a state in which a drain material with a cap is laid in the disposal site of FIG. FIG. 3 is a plan view showing a cap portion of the plastic board drain with cap that can be used as the drain material with cap of FIGS. FIG. 4 is a cross-sectional view (a) of the plastic board drain of FIG.

  As shown in FIGS. 1 and 2, the vacuum consolidation system of the present embodiment includes a water shielding sheet 15 laid on the bottom and side surfaces of a recess formed in a consolidation dewatering disposal site 10 around which a bank 11 is built, A plastic board drain (hereinafter abbreviated as “PBD”) 13 with a cap extending in the longitudinal direction and arranged in parallel as a plurality of drain materials with caps on the bottom surface with sand, and the PBD 13 with sand. And a sand mat 12 embedded so as to be covered.

  Further, the vacuum consolidation system includes a connecting pipe 14 disposed on the cap portion side of the PBD 13 and connected to the plurality of PBDs 13, a drain hose 17 connected to the connecting pipe 14 and extending beyond the embankment 11 to the outside of the embankment 11; A negative pressure device 18 comprising a vacuum pump or the like that is connected to the drain hose 17 to generate a negative pressure, and a notch tank 19 with a meter for storing water discharged from the negative pressure device 18 are provided.

  In addition, as shown in FIG. 1, soft clay G, which is the soil to be improved, is put into the concave portion of the consolidation dewatering disposal site 10 and deposited, and then covers the surface of the soft clay G as necessary. Thus, the airtight sheet 16 is laid.

  As shown in FIG. 3, the cap-equipped PBD 13 as the cap-attached drain material in FIGS. 1 and 2 has a cap portion 20 made of a plastic material or the like disposed at the end portion 13 a, and the end portion 13 a is inserted into the cap portion 20. It is fitted and sealed and fixed with a stapler 21a, an adhesive, a tape or the like. A hose 21 is integrally connected to the cap portion 20 so as to communicate with the inside of the PBD 13, and the hose 21 is connected to the connecting pipe 14.

  The cap-equipped PBD 13 is disposed on both sides of a core body 23 that is formed so as to be elongated in a flat plate shape as a whole from a porous plastic material, for example, as shown in FIGS. 3, 4 (a) and 4 (b). And a filter 24 made of a nonwoven fabric or the like. As shown in FIG. 4A, the core body 23 has a rectangular shape with a predetermined width and a long cross section. As shown in FIG. 23a is formed to extend in the longitudinal direction (perpendicular to the plane of the drawing) and has a certain degree of rigidity, and the space S formed between the partition portions 23a serves as a drainage channel to allow water to flow.

  FIG. 5 is a schematic cross-sectional view for explaining the cleaning means for the cap-equipped PBD 13 in the vacuum consolidation system of the present embodiment.

  As shown in FIG. 5, the vacuum consolidation system of the present embodiment is configured such that a compressed air cleaning device 25 made of a compressor or the like disposed on the embankment 11 can be switched to and connected to a drain hose 17. The space S in the PBD 13 can be cleaned by sending compressed air from the compressed air cleaning device 25 in a state where the portion is cut and the tip 13b of the PBD 13 is opened to the atmosphere.

  Next, FIG. 8 shows a sectional view of the disposal site 10 of FIG. 1 cut in the direction perpendicular to the paper surface. Although the preferable dimension example in a vacuum compaction system is demonstrated with reference to the figure, these dimensions are an example and it cannot be overemphasized that it can change suitably.

  The height h2 from the bottom surface of the disposal site 10 to the surface of the soft clay G of the soil to be improved is about 3 to 5 m, the thickness (height) h1 of the sand mat 12 is about 0.5 to 1 m, and the horizontal of the PBD 13 with cap The interval W in the direction is about 1 m. Further, the position in the height direction of the sand mat 12 of the cap-equipped PBD 13 may be approximately the center of the thickness h1 of the sand mat 12. The width of the PBD 13 with cap (lateral length in FIG. 4A) is about 100 mm, and the thickness (length in the vertical direction in FIGS. 4A and 4B) is about 4 mm.

  Next, the vacuum consolidation method of the present embodiment that can be implemented using the vacuum consolidation system of FIGS. 1 to 5 will be described with reference to the flowcharts of FIGS.

  FIG. 6 is a flowchart for explaining steps S01 to S10 of the vacuum consolidation method of the present embodiment. FIG. 7 is a flowchart for explaining steps S21 to S24 for executing the cleaning step S10 of FIG.

  As shown in FIGS. 1 and 2, the embankment 11 is built around and the consolidation dewatering disposal site 10 is built (S01). Next, the water shielding sheet 15 is laid on the bottom surface and the side surface of the recess of the disposal site 10 (S02).

  Next, sand is placed on the bottom surface of the disposal site 10, and a plurality of cap-equipped PBDs 13 in FIG. 3 are arranged in the longitudinal direction and covered with sand so that a plurality of cap-attached PBDs 13 are horizontally embedded. The mat 12 is formed (S03).

  Next, a soft clay G such as peat in a high water content ratio to be consolidated is put into the disposal site 10 (S03). As shown in FIG. 1, soft clay G is deposited on top of a sand mat 12 formed on the bottom surface of the disposal site 10. Next, if necessary, the airtight sheet 16 is laid so as to cover the surface of the soft clay G (S05).

  Next, as shown in FIGS. 1 and 2, the drainage hose 17 extending from the connecting pipe 14 to which the hose 21 of the PBD 13 with cap is connected is connected to the vacuum pump of the negative pressure device 18 (S06), and the negative pressure device 18 is connected. By operating and applying negative pressure to the soft clay G, consolidation dehydration is performed for a predetermined time (S07). Thereby, as shown by the arrows in FIG. 1, the pore water of the soft clay G flows to the PBD 13 with cap of the lower sand mat 12 and is discharged to the outside of the disposal site 10 through the drainage hose 17.

  Next, when the consolidation dewatering is completed, the dewatered clay G is excavated (S08), and then the solidified treatment is performed on the excavated clay in another place (S09).

  On the other hand, after excavating the clay G, the inside of the cap-equipped PBD 13 is washed (S10). That is, as shown in FIG. 5, a part of the sand mat 12 is excavated (S21), and the tip 13b of the cap-equipped PBD 13 is opened to the air (S22).

  Next, the compressed air cleaning device 25 is connected to the drain hose 17 and the compressed air is sent to the space S in the core body 23 of the PBD 13 through the drain hose 17 to clean the inside of the PBD 13 (S23).

  In the consolidation dehydration step (S07), fine clay (5 μm or less) having a fine particle size is placed on the wall of the partition portion 23a forming the space S in the core body 23 of the PBD 13 shown in FIGS. 4 (a) and 4 (b). In the cleaning step, these deposits are blown off with compressed air and discharged from the tip 13b of the PBD 13, whereby the inside of the PBD 13 is cleaned.

  Next, as shown in FIG. 1, the PBD 13 is embedded again in the sand mat 12 (S24).

  By executing the cleaning step S10 as described above, the disposal site 10 is ready to perform consolidation of the next new soft clay, and can repeat steps S04 to S10 in FIG.

  As described above, according to the vacuum consolidation method of the present embodiment, the clay G having a high water content ratio is deposited on the sand mat 12 in which the PBD 13 with cap is horizontally embedded, and then the clay G is negatively charged through the PBD 13 with cap. Since vacuum compaction is performed by applying pressure, a sufficient consolidation dewatering effect can be obtained for the clay G in a high water content ratio state. In addition, the inside of the cap-equipped PBD 13 can be cleaned with compressed air after the vacuum consolidation, and a reduction in the vacuum consolidation effect can be prevented. For this reason, since PBD13 with a cap can be repeatedly used by depositing the improvement object soil of the next new high moisture content state, and repeating the same process, consolidation dehydration can be implemented economically. .

  According to the bottom surface dewatering method of Patent Document 1, since dehydration of clay occurs only by the gravity of the clay, a sufficient amount of consolidation dewatering was not obtained, whereas according to this embodiment, a greater consolidation dewatering effect was achieved. And the period required for compaction dehydration can be shortened. For this reason, it is possible to promote effective use of clay having a high water content, which leads to improvement in economic efficiency.

  As described above, the modes for carrying out the present invention have been described. However, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in the present embodiment, the inside of the cap-equipped PBD 13 is cleaned with compressed air, but the present invention is not limited to this, and may be performed with pressurized water. That is, for example, a pressurized water generator can be installed in place of the compressed air cleaning device 25 in FIG. 5, and the pressurized water can be fed into the PBD 13 with cap through the drain hose 17 in the same manner.

  In this embodiment, a flat plastic board drain (PBD) as shown in FIG. 3 is used as the drained material with a cap. However, the present invention is not limited to this. The perforated member may be covered with a filter made of a nonwoven fabric or the like, and one end of the perforated member may be fitted into the cap portion. The shape of the cap portion is appropriately determined according to various shapes such as a cylindrical shape or a rectangular tube shape of the perforated member. As such a cylindrical perforated member, for example, a Netron (registered trademark) pipe can be used.

  Moreover, in this specification, the high water content state in the soil to be improved means that the natural water content is 200 to 1000%.

10 Consolidation dehydration disposal site, disposal site 11 Embankment 12 Sandmat 13 Plastic board drain with cap (PBD with cap)
13a End portion 13b Tip 15 Water shielding sheet 16 Airtight sheet 17 Drain hose 18 Negative pressure device 20 Cap portion 25 Compressed air cleaning device G Soft clay (Soil to be improved)

Claims (3)

A vacuum consolidation method for dehydrating the soil to be improved in a high water content state by vacuum consolidation,
Laying a water shielding sheet on the bottom and side of the disposal site;
Forming a sand mat with a drain material with a cap embedded horizontally on the bottom surface;
Depositing the soil to be improved in a high moisture content state on the sand mat;
Performing vacuum consolidation by applying a negative pressure to the soil to be improved through the drained material with cap;
Excavating the soil to be improved after the vacuum consolidation;
Cleaning the inside of the capped drain material with a compression medium,
A vacuum consolidation method characterized by repeatedly performing the deposition step and the vacuum consolidation step on a new soil to be improved in a high water content state after the cleaning step.   2. The vacuum consolidation method according to claim 1, wherein compressed air or pressurized water is used as the compression medium, and the cleaning step is performed by connecting a compressed air device or a pressurized water device to a drain hose connected to the drained material with a cap.   The vacuum consolidation method according to claim 1 or 2, wherein the vacuum consolidation is performed after the surface of the soil to be improved is covered with an airtight sheet.

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