JP2016014256A - Vacuum consolidation method combined with banking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum consolidation method combined with banking for improving a soft ground that allows a cap-type vacuum consolidation method to be applied efficiently, even to a soft ground for which an impermeable layer cannot be secured in a ground surface layer, when vacuum consolidation and banking are used in combination.SOLUTION: A vacuum consolidation method combined with banking for improving a soft ground uses a drain material 12 having an impermeable cap part 12a formed at a top part, a flexible drain hose 12b that extends from a top edge of the cap part, and a drain part 12c extending downward from the cap part, and comprises the following steps of: installing a plurality of the drain materials in a longitudinal direction in a ground G to be improved, keeping the cap part above a ground surface S; connecting the drain hose to a plurality of water collecting pipes 13 installed on the ground surface; air-tightly covering the entire ground to be improved with a double-face protection air-tight sheet 11 having both surfaces protected; applying a negative pressure on the drain material from a negative pressure source P, through the water collecting pipe; and placing a banking 15 on the double-face protection air-tight sheet.

Description

  The present invention relates to an embankment combined vacuum consolidation method for improving soft ground.

  A vacuum consolidation method is known as a consolidation improvement method for soft clay ground. This construction method improves the consolidation by applying a negative pressure to the clay layer, and is roughly divided into a sheet type as shown in FIG. 6 (for example, see Non-Patent Document 1) and a cap type as shown in FIG. And Patent Document 1 and Non-Patent Document 2). The construction method of the sheet type method is to place a plastic board drain as a drain material in the ground, and then place a water collecting pipe consisting of a porous pipe on the ground surface, connect one end to the negative pressure source P, and cover the water collecting pipe After the sand mat is installed in this way, the ground surface is covered with an airtight sheet, and the water discharged from the clay layer by the negative pressure action of a negative pressure source such as a vacuum pump is discharged through the sand mat and the water collecting pipe. It is guided to the pressure source P and discharged to the outside.

  On the other hand, the construction method of the cap type construction method is to place a PBD with a cap in the ground as shown in Fig. 7, and connect the drainage hose previously attached to the PBD with a cap to a negative pressure source via a water collection pipe. The discharged water from the clay layer is guided from the plastic board drain to the negative pressure source P through the drain hose and discharged to the outside. The sheet type construction method in Fig. 6 needs to cover the ground surface with an airtight sheet, so it is intended for construction on land (in the air), whereas the cap type construction method in Fig. 7 is in coastal area (underwater) ) Is also possible.

JP 2006-291645 A JP 2010-37831 A

High vacuum N & H method technical data (issued by Vacuum Consolidation Technology Association) Vacuum Consolidation Drain Method Technical Document (Published by Vacuum Consolidation Drain Method Study Group, May 2011)

  When combined with vacuum consolidation using the cap method during embankment construction, the stability during embankment construction is greatly improved and the fill rate of the embankment is 20 to 30 cm / day (about 5 to 10 cm / day if vacuum consolidation is not used together) (See Non-Patent Document 2). The reason for this is that the negative pressure is an inward isotropic pressure, so the displacement at the boundary of the improvement zone is directed inward toward the improvement side (safe side), whereas the displacement due to the embankment load is outward (Non-safe side) The directions of both displacements are contradictory to each other. However, the displacements that are contradictory to each other are offset in this way, and the displacement as a whole can be kept small (see, for example, Patent Document 2).

Further, from the viewpoint of effective securing of the negative pressure effect in the cap-type method, the impermeable layer permeability of about 1m thick on the ground surface layer portion consisting of silt-clay 10 ^-7 m / s as the airtight layer It is necessary to secure. Usually, as shown in FIG. 7, a portion of a depth of about 1 m from the ground surface of the clay layer to be improved is used as the hardly permeable layer SL. However, if such a poorly permeable layer cannot be secured, it is necessary to newly construct a difficultly permeable layer with a thickness of about 1 m on the ground surface by embankment with clayey material, etc. Therefore, under these conditions, the cap type construction method The application of was not efficient.

  In the construction using both vacuum compaction and embankment, it is conceivable to cope with a case where a hardly water-permeable layer cannot be secured in the ground surface layer portion as described above by using an airtight sheet as shown in FIG. However, the problem in this case is that there is no sand mat on the underside of the airtight sheet, so there is a risk of damage to the airtight sheet such as embankment material such as gravel on the embankment hits the airtight sheet during embankment construction. For this reason, the airtightness of the airtight sheet cannot be maintained, and the efficiency of vacuum compaction is reduced.

  In view of the above-mentioned problems of the prior art, the present invention can efficiently apply the cap-type vacuum consolidation method even in soft ground where a hard-permeable layer cannot be secured in the ground surface layer portion when vacuum consolidation and embankment are used in combination. Another object is to provide a vacuum consolidation method combined with embankment for improving soft ground.

The embankment combined vacuum consolidation method for achieving the above object includes an impervious cap provided at the top, a flexible drain hose extending from the upper end of the cap, and a drain extending downward from the cap. A vacuum consolidation method combined with embankment for soft ground improvement using a drain material having a part,
A step of placing a plurality of the drain materials in the vertical direction so that the cap portion is positioned on the ground surface with respect to the ground to be improved;
Connecting the drain hose to a plurality of water collecting pipes disposed on the ground surface;
A step of airtightly covering the entire ground to be improved with a double-sided protective airtight sheet with both sides protected;
Applying a negative pressure to the drain material from a negative pressure source via the water collecting pipe;
Embedding on the double-sided protective airtight sheet.

  According to this embankment combined vacuum consolidation method, drain material is placed on the ground to be improved, and the cap portion is positioned on the ground surface, and the entire ground is covered with a double-sided protective airtight sheet. Since airtightness can be maintained, it is not necessary to construct a new poorly permeable layer even in a ground where a hardly permeable layer cannot be secured in the ground surface layer portion, and the vacuum consolidation method can be efficiently applied. Moreover, since the cap part is located on the ground surface, the upper end of the drain part is located directly below the ground surface, and therefore vacuum consolidation can be performed from directly below the ground surface.

  In addition, even if embankment is carried out on the double-sided protective airtight sheet, the upper surface of the airtight sheet is protected, so that the risk of damage to the airtight sheet due to hitting of the embankment material and the load from the embankment is reduced, and on the ground surface. Since the lower surface of the double-sided protective airtight sheet is protected even if there are irregularities due to caps, water collecting pipes, drain hoses, etc., the risk of damage to the airtight sheet due to irregularities on the ground surface is reduced. Therefore, airtightness by the airtight sheet can be maintained, and the efficiency of vacuum compaction does not decrease. In addition, since the drainage hose is flexible, it may be crushed by the load from the embankment, but since a double-sided protective airtight sheet exists between the embankment and the drainage hose, the drainage hose can be prevented from being crushed, The drainage by the drainage hose can be maintained.

  In the embankment combined vacuum consolidation method, it is preferable to use a double-sided protective airtight sheet in which net sheets are bonded to both sides of an airtight sheet.

  Moreover, it is preferable to start the embankment process after applying a negative pressure for a predetermined time in the negative pressure operation process.

  According to the present invention, by using vacuum compaction and embankment in combination, it is possible to efficiently apply a vacuum consolidation method using a drain material having a cap part even in soft ground where a hard-permeable layer cannot be secured on the ground surface layer part. An embankment combined vacuum consolidation method for improving soft ground can be provided.

It is a flowchart for demonstrating process S01-S09 of the embankment combined use vacuum compaction method by this embodiment. It is the top view (a) and sectional drawing (b) which show the double-sided protection airtight sheet | seat used for the embankment combined use vacuum consolidation method of FIG. It is a schematic longitudinal cross-sectional view of the ground for demonstrating process S02-S06 of FIG. It is a schematic plan view of the ground for demonstrating process S03-S06 of FIG. It is a schematic longitudinal cross-sectional view of the ground for demonstrating process S07 of FIG. 1, and S08. It is the schematic for demonstrating the conventional sheet | seat type vacuum consolidation method. It is the schematic for demonstrating the conventional cap type vacuum consolidation method.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a flowchart for explaining the steps S01 to S09 of the vacuum consolidation method according to the present embodiment. FIG. 2 is a plan view (a) and a cross-sectional view (b) showing a double-sided protective airtight sheet used in the embankment combined vacuum consolidation method of FIG. FIG. 3 is a schematic longitudinal sectional view of the ground for explaining steps S02 to S06 in FIG. FIG. 4 is a schematic plan view of the ground for explaining steps S03 to S06 in FIG. FIG. 5 is a schematic longitudinal sectional view of the ground for explaining the steps S07 and S08 of the embankment combined vacuum consolidation method of FIG. 3 and 5, the protective net sheets 2 and 3 of the double-sided protective airtight sheet 11 are shown in an emphasized manner.

  With reference to FIG. 1, first, a double-sided protective airtight sheet 11 used in the embankment combined vacuum consolidation method according to the present embodiment is prepared (S01). For example, as shown in FIGS. 2A and 2B, the double-sided protective airtight sheet 11 includes a highly airtight sheet 1 and a protective net sheet 2 attached to the lower and upper surfaces of the airtight sheet 1 with an adhesive or the like. , 3.

  The hermetic sheet 1 is made of, for example, polyethylene or vinyl chloride, and the thickness is preferably about 0.5 to 2.0 mm. The protective net sheets 2 and 3 are preferably made of a material having a mesh shape or a lattice shape and a tensile strength of 29 kN / m or more. For example, the protective net sheets 2 and 3 can be made of aramid fiber, high-strength polyester, etc. is not. In the double-sided protective airtight sheet 11, the airtight sheet 1 is protected and reinforced by the protective net sheets 2 and 3 on both sides thereof to prevent breakage.

  Next, as shown in FIG. 3, a water-impermeable cap portion 12a provided at the top, a flexible drain hose 12b extending from the tip, and a suction drainage in the ground extending below the cap portion 12a. A plastic board drain 12 (hereinafter referred to as “capped drain material 12”) having a drain portion 12c for carrying out the vertical movement into the ground G to be improved by a placement machine in a square arrangement of 1.0 m × 1.0 m. Placing (S02). At this time, the cap part 12a corresponding to the connection part between the drain part 12c and the drainage hose 12b is located on the ground surface S. The ground G to be improved is a soft viscous ground.

  The drain part 12c is comprised from the core material which consists of plate-shaped plastics, and the filter which consists of a nonwoven fabric etc. which are arrange | positioned around the core material. A specific example of the drained cap material 12 is described in, for example, Japanese Patent Application Laid-Open No. 2006-241872.

  Next, as shown in FIG. 3, the flexible drain hose 12 b of the drained material 12 with the cap on the ground surface S is connected to the water collecting pipe 13 disposed on the ground surface S as shown in FIG. 4. (S03). As shown in FIG. 4, the water collection pipe 13 is connected to a negative pressure source P including a vacuum pump or the like through a header pipe 14 disposed in the center.

  Next, as shown in FIGS. 3 and 4, the entire ground is covered with the double-sided protective airtight sheet 11 (S04). Next, as shown in FIG. 3, the end portion 11a of the double-sided protective airtight sheet 11 is embedded in the ground G, and this embedded portion is sealed with viscous soil (S05). The embedding depth d is preferably about 1.5 m, for example.

  By the steps S04 and S05, the cap portion 12a, the drainage hose 12b, the water collecting pipe 13 and the like on the ground surface S can be covered with the double-sided protective airtight sheet 11, and the inside thereof can be made airtight. In addition, as shown in FIG. 4, for example, a 60 m × 50 m ground plane range can be set as a ground improvement target, but this is an example and can be changed as appropriate.

  Next, as shown in FIGS. 3 and 4, the negative pressure source P is operated to apply a negative pressure to the ground G (S06).

  After negative pressure is applied for a predetermined period (for example, one week), embankment is started as shown in FIG. 5 (S07). For example, the target height of the embankment is 5 m, the thickness is 30 cm per day per layer, and the embankment can be carried out by directly unloading the mountain soil mixed with 20% gravel with a bulldozer (total weight 3940 kg). . The negative pressure action continues during the embankment construction.

  As shown in FIG. 5, when the embankment 15 reaches a target height (for example, 5 m), the embankment construction is completed, and then the negative pressure and consolidation with the embankment are continued for a predetermined period (for example, about 3 months) (S08). . Thereby, the water from the ground G is discharged to the outside of the negative pressure source P, and the consolidation of the ground G proceeds.

  After completion of the negative pressure and the consolidation by the embankment, the negative pressure source P such as the vacuum pump of FIG. 4 and FIG. 5 and a part of the header pipe 14 are removed (S09).

  As described above, according to the embankment combined vacuum consolidation method of the present embodiment, even if the ground G is a soft ground where a hard-permeable layer cannot be secured on the ground surface layer part, the entire ground to be improved is improved by the double-sided protective airtight sheet 11. By keeping the inside of the double-sided protective airtight sheet 11 airtight by covering hermetically, there is no need to newly build a poorly water-permeable layer by embankment with a clay material or the like, and a cap-type vacuum consolidation method using a drained material 12 with a cap is used. It can be applied efficiently and is economical.

  Further, it is not necessary to apply a sand mat necessary for the conventional sheet type construction method shown in FIG. Moreover, since the cap part 12a of the drained material 12 with a cap is located on the ground surface S, the upper end of the drain part 12c is located directly under the ground surface S. Therefore, vacuum consolidation is performed from directly under the ground surface S. it can.

  Conventionally, water discharged from the cohesive land by consolidation is guided to the vacuum pump room through a drain hose connected to each drain material. Could be crushed and could not drain. Further, the airtight sheet is also damaged under the same embankment loading action, and there is a possibility that the inside of the airtight sheet cannot be kept airtight.

  Therefore, in the present embodiment, as shown in FIGS. 2A and 2B, the upper surface is obtained by using the double-sided protective airtight sheet 11 in which the protective net sheets 2 and 3 for preventing damage are attached to the upper and lower surfaces of the airtight sheet 1. The airtight sheet 1 can be protected by a protective net sheet 3 on the upper surface against a load (unevenness) such as embankment from or from hitting a embankment material such as gravel. Further, even if there are irregularities due to the cap portion 12a, the water collecting pipe 13, the drainage hose 12b, etc. on the ground surface S, the airtight sheet 1 can be protected by the protective net sheet 2 on the lower surface.

  Further, the drainage hose 12b located below the double-sided protective airtight sheet 11 is protected by the protective net sheets 2 and 3 of the double-sided protective airtight sheet 11, thereby preventing the drainage hose 12b from being crushed due to a banking load or the like. The water flow cross-sectional area of the hose 12b can be secured, and the drainage by the drainage hose 12b can be maintained.

  As described above, the double-sided protective airtight sheet 11 prevents the airtight sheet 1 from being damaged by the double-sided protective airtight sheet 11 with respect to the embankment load on the upper surface, the contact with the embankment material, and the unevenness on the ground surface of the lower surface. Since the inside of 1 can be kept airtight, the efficiency of the vacuum consolidation method using the drained cap material 12 can be maintained.

  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 FIG. 1, the negative pressure operation step S06 is started prior to the embankment step S07, but the present invention is not limited to this, and both steps S06 and S07 may be started almost simultaneously.

  In this embodiment, as shown in FIGS. 2 (a) and 2 (b), the double-sided protective airtight sheet 11 is formed by bonding the protective net sheets 2 and 3 to the airtight sheet 1, but the present invention is not limited thereto. For example, another type of protective sheet may be provided on both surfaces of the airtight sheet.

  According to the embankment combined vacuum consolidation method using the vacuum consolidation and embankment of the present invention, the vacuum consolidation method using the drain material having the cap portion can be efficiently used even in soft ground where a hard-permeable layer cannot be secured on the ground surface layer portion. Since it can be applied, soft ground improvement can be carried out efficiently.

DESCRIPTION OF SYMBOLS 1 Airtight sheet | seat 2,3 Protective net sheet | seat 11 Double-sided protective airtight sheet | seat 11a End part 12 Plastic board drain, Drain material with a cap 12a Cap part 12b Drain hose 12c Drain part 13 Drain pipe 15 Filling G Ground P Negative pressure source S Ground surface SL Impermeable layer

Claims (3)

Soft ground improvement using a drain material having an impervious cap provided at the top, a flexible drain hose extending from the upper end of the cap, and a drain extending downward from the cap A vacuum consolidation method combined with embankment for
A step of placing a plurality of the drain materials in the vertical direction so that the cap portion is positioned on the ground surface with respect to the ground to be improved;
Connecting the drain hose to a plurality of water collecting pipes disposed on the ground surface;
A step of airtightly covering the entire ground to be improved with a double-sided protective airtight sheet with both sides protected;
Applying a negative pressure to the drain material from a negative pressure source via the water collecting pipe;
And a step of embedding on the double-sided protective airtight sheet.   2. The embankment combined vacuum consolidation method according to claim 1, wherein the double-sided protective airtight sheet uses a net sheet bonded to both sides of an airtight sheet.   The embedding combined use vacuum consolidation method according to claim 1 or 2, wherein the embedding step is started after a negative pressure is applied for a predetermined time in the negative pressure acting step.

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