JP2023164694A - Construction method of ground for liquefaction countermeasure - Google Patents

Abstract

To provide a construction method of the ground for liquefaction countermeasure allowing the liquefaction countermeasure to be done without deteriorating rigidity of the ground and excellent in workability.SOLUTION: A construction method of the ground for liquefaction countermeasure is configured to bury a plurality of drain members 1 placed apart from each other in a lateral direction in the ground for the liquefaction countermeasure. The drain member is provided with: a perforated pipe placed in the center; a drain sheet 3 wounded around the perforated pipe 2; and an outer periphery filter in a cylindrical shape placed on an outer periphery of the wounded drain sheet. And, in a process of drawing the drain member from a lower end opening of a mandrel 61, a lower end of a wire rope 63 passing through an inner cavity of the mandrel is connected to an end part of the perforated pipe and the drain member in a bent state is drawn into from a gap between the ground and the lower end opening by winding up the wire rope.SELECTED DRAWING: Figure 6

Description

The present invention relates to a method for constructing a liquefaction prevention ground using a liquefaction prevention drain material buried in the ground to prevent liquefaction.

In order to prevent the ground from liquefying in the event of a large-scale earthquake, a method is known in which drain materials with high drainage performance are placed at predetermined intervals in the ground that is likely to liquefy. (See Patent Documents 1-3, etc.).

In the liquefaction countermeasure method disclosed in Patent Documents 1 to 3, a synthetic resin drain material is buried vertically in the ground, and excess pore water pressure generated during an earthquake is quickly dissipated by the drain material, thereby preventing liquefaction. to prevent

For example, in Patent Document 1, a large number of vertically oriented cylindrical drain members are arranged at intervals in the horizontal direction to take measures against liquefaction in a construction area that is spread out over a surface area. As the cylindrical drain material, a synthetic resin filter material formed into a cylindrical shape or a hollow pipe such as a vinyl chloride pipe with a large number of permeable holes perforated in the peripheral wall are used.

In addition, the drain material disclosed in Patent Document 2 is made of semi-rigid vinyl chloride resin or the like and is formed into a hollow rectangular cross-section, and cannot be rolled into a roll. are buried to a predetermined depth while being connected using connecting tools at the pouring site.

On the other hand, in the liquefaction countermeasure construction method of Patent Document 3, liquefaction countermeasures are achieved by connecting, for example, four water-permeable vanes made of belt-shaped synthetic resin plates covered with a covering material such as a net to form a cross shape in plan view. Push it into the required ground.

Japanese Patent Application Publication No. 2015-169045 Japanese Patent Application Publication No. 2012-241385 Patent No. 2743031

However, if a large number of hollow drain materials are placed in the ground, there is a risk that the rigidity of the ground will decrease over the entire area where they are placed, and even if excess pore water pressure can be dissipated in the event of a large-scale earthquake, There is a problem in that ground deformation occurs due to a decrease in rigidity.

In addition, the drain material with a rectangular cross section as disclosed in Patent Document 2 is hard and cannot be rolled up, resulting in increased transportation costs and troublesome connection work, and the rectangular cross section has high resistance, so it cannot be buried in the ground. There are construction issues, such as being difficult to install.

Therefore, an object of the present invention is to provide a method for constructing a liquefaction countermeasure ground that can be implemented without reducing the rigidity of the ground and has excellent workability.

In order to achieve the above object, the liquefaction countermeasure ground construction method of the present invention provides a liquefaction countermeasure drain material buried in the ground for liquefaction countermeasures, which includes a perforated pipe placed in the center and , a liquefaction system comprising: a drainage sheet formed of a high-rigidity geosynthetic drainage material with an embossed structure wrapped around the perforated pipe; and a cylindrical outer peripheral filter disposed around the outer periphery of the wrapped drainage sheet. Use drain material as a countermeasure.

and a step of drawing the liquefaction countermeasure drain material having a conical anchor portion attached to the tip into the inner space of the mandrel attached to the casting machine from the lower end opening of the mandrel, and The step of drawing the liquefaction countermeasure drain material from the lower end opening of the mandrel comprises a step of pushing the drain material for countermeasures into the ground, and a step of pulling out the mandrel after the anchor part reaches a predetermined depth. , the lower end of the wire rope passed through the interior of the mandrel is connected to the end of the perforated pipe of the liquefaction prevention drain material, and the wire rope is rolled up to remove the wire from the gap between the ground surface and the lower end opening. It is characterized in that the drain material for liquefaction countermeasures in a bent state is drawn in.

Here, the casting machine has at least one of a vibrator and a high-pressure water jet section, and the step of pushing the liquefaction prevention drain material into the ground is performed by applying vibrations to the mandrel by the vibrator. It may be configured such that at least one of application and jetting of high-pressure water from the jet section is performed.

Further, the drainage sheet may have a configuration in which the shape of the drainage sheet is maintained by a shape-retaining band. Furthermore, it can be configured to include a water-permeable shape-retaining sheet formed in a laminated structure with the highly rigid geosynthetics drainage material.

Further, the drainage sheet may be wound two to four times. Furthermore, a plurality of shorter drainage sheets may be arranged for the long perforated pipe.

The drain material for liquefaction prevention used in the present invention configured as described above includes a perforated pipe placed in the center, a drainage sheet formed of a highly rigid drainage material wrapped around the perforated pipe, and a drainage sheet placed around the outer periphery of the perforated pipe. It is equipped with a cylindrical outer peripheral filter.

Therefore, a plurality of drainage paths are formed by the perforated pipe and the drainage sheet wrapped around the perforated pipe, and it is possible to quickly dissipate excess pore water pressure and prevent liquefaction. In addition, since a highly rigid drain material is formed by the perforated pipe and the surrounding drainage sheet, the rigidity of the ground will not be reduced even if a large number of drains are buried.

Furthermore, if the drain material is formed in a cylindrical shape, it is easy to cast and has excellent workability. Further, since the cylindrical outer peripheral filter is arranged around the outer periphery of the wrapped drainage sheet, clogging of the drainage path of the drain material can be made less likely to occur.

Furthermore, even if the drainage sheet is shortened to make it easier to transport or bend as a drain material, if it is housed in a cylindrical outer filter, it can be used as a drain material even during work at the pouring site. It is possible to maintain gender.

By burying such drain materials for liquefaction prevention in the ground at intervals in the lateral direction, it is possible to create a liquefaction prevention ground structure that does not reduce the rigidity of the ground. In addition, water can be collected by connecting the upper ends of perforated pipes of drain material for liquefaction countermeasures placed at intervals in the horizontal direction with perforated pipes of drain material facing in the horizontal direction. Pore water can be quickly treated as wastewater.

The invention of the construction method for liquefaction prevention ground is that when the liquefaction prevention drain material is pushed into the ground while applying vibration to the mandrel with a vibrator or jetting high-pressure water from the jet part, it is necessary to In some cases, the density of the ground can be increased and the amount of residual settlement after excess pore water pressure dissipated can be reduced. Furthermore, by drawing the bent liquefaction prevention drain material through the gap between the ground surface and the lower end opening of the mandrel, even if the liquefaction prevention drain material becomes long, it can easily fill the inside of the mandrel. can be inserted.

BRIEF DESCRIPTION OF THE DRAWINGS It is a perspective view explaining the structure of the liquefaction prevention ground structure in which the drain material of embodiment of this invention is buried. FIG. 1 is a perspective view illustrating the structure of a drain material according to an embodiment of the present invention. It is a process diagram explaining the manufacturing method of a drainage sheet. (a) is an explanatory view showing the packing form of the drainage sheet, and (b) is an explanatory view showing the external appearance of the outer peripheral filter. It is a process diagram explaining the manufacturing method of a drain material. It is a process diagram explaining the operation|work of setting a drain material in a casting machine. It is a process diagram explaining the work of driving a drain material into the ground. It is a figure conceptually explaining the density increase effect by vibration casting and high-pressure water injection. FIG. 2 is a cross-sectional view illustrating a configuration in which a horizontal drain member is connected to a vertically buried drain member. 1 is a perspective view illustrating the structure of a drainage sheet of Example 1. FIG. FIG. 2 is a perspective view illustrating the structure of the drain material of Example 1.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating the configuration of a liquefaction prevention ground structure in which a drain material 1, which is a drain material for liquefaction prevention according to the present embodiment, is buried, and FIG. 2 is a diagram illustrating the configuration of the drain material 1 in detail. FIG.

The drain material 1 of this embodiment is buried in the ground G as a countermeasure against liquefaction. That is, the drain materials 1 are pushed into the ground G in the vertical direction (see FIG. 7), and are arranged in large numbers in the construction area at intervals in the horizontal direction.

Here, the length of the drain material 1 is set according to the depth of the liquefaction layer of the liquefaction prevention ground. Further, the lateral placement interval of the drain material 1 is set by design to a value that can efficiently dissipate excess pore water pressure generated by an assumed earthquake.

As shown in FIG. 2, the drain material 1 of this embodiment includes a perforated pipe 2 arranged at the center, a drainage sheet 3 wrapped around the perforated pipe 2, and a drainage sheet 3 wrapped around the perforated pipe 2. It is mainly constituted by a cylindrical outer peripheral filter 4 arranged therein.

The perforated tube 2 is a flexible cylindrical tube made of synthetic resin material (geosynthetics) or the like. For example, a long flexible tube such as a CD tube can be used. Then, a perforated pipe 2 is obtained by punching a large number of holes in the peripheral wall of the cylindrical pipe material. For example, a perforated tube 2 with a diameter of about 3 cm can be used.

On the other hand, the drainage sheet 3 is formed into a laminated structure of a plate-shaped highly rigid drainage material 31 and a water-permeable shape-retaining sheet 32, as shown in FIG. The high-rigidity drainage material 31 is a sheet-like member (high-rigidity geosynthetics drainage material) in which geosynthetics having high rigidity is formed into an uneven surface portion 311, as shown in an enlarged view at the left end of FIG. .

The highly rigid drainage material 31, which is formed into an embossed structure such as the uneven surface portion 311 using a hard synthetic resin material, has flow channels formed in various in-plane directions. Further, the highly rigid drainage material 31 is provided with a plurality of water passage holes 312, . . . that pass through the front and back sides of the face material. Groundwater or the like can now permeate through the water passage hole 312.

A shape-retaining sheet 32 having the same size in plan view is attached to the highly rigid drainage material 31 formed into a rectangle. Therefore, the flow path of the highly rigid drainage material 31 becomes a flow path along the shape-retaining sheet 32.

The shape-retaining sheet 32 is a shape-retaining portion that is attached to maintain the shape of the highly rigid drainage material 31 . That is, as shown at the right end of FIG. 3, in order to prevent the highly rigid drainage material 31 from bending when the drainage sheet 3 is vertically erected, a shape-retaining sheet 32 is attached to form a laminated structure. Moreover, by laminating the shape-retaining sheets 32, the shape of the wrapped drainage sheet 3 can be easily maintained. For such a shape-retaining sheet 32, a material that can also be expected to have a filter function, such as a nonwoven fabric, can be used.

Although FIG. 3 shows a rectangular drainage sheet 3 with a vertical length of 1 m, the drainage sheet 3 is not limited to this, and any length can be used. When using a short drainage sheet 3 as described later, one with a length of, for example, about 1.0 m to 1.5 m can be used.

Such a band-shaped drainage sheet 3 is wound around a cylindrical core material 33 during manufacture. The number of times the drainage sheet 3 is wound can be arbitrarily set from about 2 to 4 turns. FIG. 4(a) shows the packaging of the three-turn drainage sheet 3 from which the central core material 33 has been removed.

On the other hand, FIG. 4(b) shows the appearance of a cylindrical outer peripheral filter 4 in which a hollow portion 41 accommodates a cylindrical drainage sheet 3. As shown in FIG. The outer peripheral filter 4 can be formed of water-permeable nonwoven fabric or the like. This outer peripheral filter 4 can also be shaped like a bag with a bottom.

The outer peripheral filter 4 is formed to have a continuous length that is approximately the same as the length to be buried in the ground G as the drain material 1. In FIG. 4(b), the outer circumferential filter 4 is shown having a length of 10 m, but the outer circumferential filter 4 is not limited to this, and may be formed to have a designed required length. Furthermore, the diameter of the outer peripheral filter 4 is not limited to 0.1 m, and can be arbitrarily set to about 0.09 m to 0.11 m.

As shown in FIG. 2, the outer peripheral filter 4 forms the outer peripheral surface of the drain material 1. Two drainage routes in the vertical direction are formed by the drainage sheet 3 wound around two to four times, housed in the outer peripheral filter 4, and the perforated pipe 2.

In short, when excessive pore water pressure is generated around the drain material 1 due to an earthquake, pore water infiltrates from the outer peripheral filter 4 toward the drainage sheet 3, and water passes through the water passage holes 312 between the circulating drainage sheets 3. Moving. Then, drainage treatment in the vertical direction is carried out through the channels of the drainage sheet 3 formed along the shape-retaining sheet 32.

Furthermore, the interstitial water that has flowed into the drainage sheet 3 flows from the lower end opening of the perforated pipe 2, ascends the perforated pipe 2, and is subjected to drainage treatment in the vertical direction. Further, the water may flow into the pipe through a hole in the peripheral wall of the perforated pipe 2 adjacent to the drainage sheet 3 and be treated as wastewater by the perforated pipe 2. In this way, by performing wastewater treatment using two drainage channels with wide cross sections, excess pore water pressure can be quickly dissipated.

Since two drainage routes are secured, the diameter of the perforated pipe 2 can be made smaller compared to the case where only a conventional cylindrical drain material is arranged. For example, if a conventional cylindrical drain material needs to have a diameter of about 8 cm, the diameter of the perforated tube 2 can be reduced to about 3 cm.

Furthermore, since the drainage sheet 3 to be circulated is formed of a highly rigid drainage material 31, the drainage material 1 composed of the perforated pipe 2 with a relatively small diameter and the highly rigid drainage sheet 3 can be used to drain the ground G. Even if it is placed in place of soil, the rigidity will not decrease.

Next, a method for manufacturing the drain material 1 of this embodiment will be described with reference to FIGS. 4 and 5. First, a plurality of short, rolled-up drainage sheets 3 are manufactured. This drainage sheet 3 is manufactured by wrapping the unfolded drainage sheet 3 as shown in the center of FIG. can.

In the rolled-up drainage sheet 3, the edges of the shape-retaining sheet 32 are joined with an adhesive or the like so that it does not spread out by itself, and the core material 33 is removed. The drainage sheet 3 wound into a roll has a short cylindrical shape with a height of about 1.0 m to 1.5 m, so it can be efficiently transported to the pouring site by truck or the like.

On the other hand, although the cylindrical outer filter 4 is long, it is made of nonwoven fabric and can be rolled up or folded, so it can be efficiently transported to the casting site by truck or the like. Further, since the perforated pipe 2 having a length comparable to that of the outer peripheral filter 4 is flexible, it is transported to the casting site in a wound state.

Subsequently, at the casting site, as shown in FIG. 5(a), the tip of the perforated pipe 2 is attached to a conical anchor plate 5 formed of a steel plate or the like, which serves as an anchor part. Then, the outer filter 4 is placed around the perforated tube 2, and the tip of the outer filter 4 is bonded to the anchor plate 5 with an adhesive or the like.

As shown in FIG. 5(b), a roll-shaped short drainage sheet 3 transported to the casting site is inserted into the hollow part 41 of the outer peripheral filter 4 in which the perforated pipe 2 is arranged at the center. The drainage sheet 3 is moved to the position of the anchor plate 5 by passing the perforated tube 2 through the hole in the center of the roll.

Similarly, short drainage sheets 3 are successively inserted into the hollow part 41 of the outer peripheral filter 4, and the drainage sheets 3 are arranged in order from the anchor plate 5 side, as shown in FIG. 5(c). This operation is continued until the hollow part 41 of the outer peripheral filter 4 is filled with the drainage sheets 3, . . . as shown in FIG. 5(d).

Next, with reference to FIGS. 6 to 8, a method for constructing a liquefaction prevention ground according to the present embodiment, in which the manufactured drain material 1 is cast into the ground G, will be described. A casting machine 6, 6A as shown in FIG. 6 or 8 is used to cast the drain material 1, but since it is a well-known machine, a brief explanation will be provided.

The pouring machine 6 shown in FIG. 6A is movable with a crawler and includes a leader 62 and a slider 621 that can be raised and lowered along the leader 62. The leader 62 can be erected vertically, and the mandrel 61 is supported by the slider 621.

The mandrel 61 is a cylindrical rod tube having an inner diameter slightly larger than the outer diameter of the drain material 1, and a wire rope 63 suspended from the upper end of the leader 62 is passed through the inside. Then, the lower end of the wire rope 63 is connected to the end of the perforated pipe 2 of the drain material 1 carried to the casting site.

When inserting the drain material 1 into the interior of the mandrel 61, the mandrel 61 is first pulled up so that there is a gap of about 1 m between it and the ground surface. Subsequently, the wire rope 63 is wound up and the upper part of the drain material 1 is drawn into the lower end opening of the mandrel 61, as shown in FIG. 6(b).

Here, since the drain material 1 is composed of a flexible perforated pipe 2, an outer peripheral filter 4, and a plurality of short drainage sheets 3, etc., when inserting it into the mandrel 61, It can be bent and pulled in. That is, even if each of the drainage sheets 3 is hard and does not bend, it can be bent in the gap between the drainage sheets 3, 3.

The anchor plate 5 attached to the tip of the drain material 1 has the maximum diameter of the cone larger than the inner diameter of the mandrel 61, so the anchor plate 5 is caught on the lower end of the mandrel 61 and the drain material The insertion of No. 1 into the mandrel 61 is stopped.

Subsequently, as shown at the left end of FIG. 7, the anchor plate 5 is thrust into the ground G, and the mandrel 61 is pushed down by the slider 621, thereby pushing the drain material 1 together with the mandrel 61 into the ground G. That is, when the mandrel 61 is pushed down, its lower end pushes the anchor plate 5, and the drain material 1 is pushed down together with the mandrel 61.

Here, when using a casting machine 6A equipped with a vibrator 64 and a jet section 65 as shown in FIG. can give.

When vibro (vibration 64a) is applied to the ground G, if it is a saturated, loose sand layer, the soil particles will settle like they are falling underwater, the sedimentary structure will be rebuilt, the density will increase, and it will resist liquefaction. The undrained strength of the ground G can be increased.

Furthermore, jetting high pressure water 65a from a jet section 65 provided at the tip of the mandrel 61 can also be used. Alternatively, only the jet portion 65 may jet the high-pressure water 65a.

When vibration compaction is performed using vibrators, water jets (high-pressure water injection), etc., a volume change (volume reduction G1) occurs in the ground G, as shown in the lower part of Figure 8, and the density of the ground G increases. increases, so it is possible to create a ground structure that can suppress residual settlement.

Pushing of the mandrel 61 into the ground G continues until the anchor plate 5 reaches a predetermined depth determined by design or the like. After the drain material 1 is pushed into the ground G in this manner, only the mandrel 61 is pulled out from the ground G by raising the slider 621.

When the mandrel 61 is pulled out, the drain material 1 with the anchor plate 5 attached to its tip is vertically buried in the ground G, as shown at the right end of FIG. FIG. 1 shows a state after construction in which drain materials 1, . . . are repeatedly poured while moving the pouring machine 6 (6A) in the lateral direction.

The upper ends of the drain material 1 protruding from the ground G where liquefaction countermeasure work has been performed are connected by a horizontal pipe (not shown) or the like. That is, the water that has risen through the perforated pipe 2 is quickly drained through the horizontal pipe.

On the other hand, as shown in FIG. 9, a horizontally drawn drain material 1A, which is a drain material for preventing liquefaction and has the same structure as the drain material 1, can be used as a horizontally drawn pipe. The horizontal drain material 1A is arranged, for example, in the horizontal direction in order to connect the upper ends of the vertically cast drain materials 1 so as to allow water to pass therethrough.

The horizontal drain material 1A has a larger diameter than the vertical drain material 1. For example, if the diameter of the drain material 1 is about 100 mm, the horizontal drain material 1A having a diameter of about 150 mm is used.

The perforated pipe 2 protruding from the upper end of the drain material 1 and the perforated pipe 2A protruding from the side of the horizontal drain material 1A are connected by a T-shaped, L-shaped, or cross-shaped joint material 21. be done. The periphery of the horizontal drain material 1A arranged in this manner is filled with single-grain crushed stones, etc., to form a crushed stone layer R1 with a thickness of about 300 mm. Moreover, a roadbed layer R2, an asphalt layer R3, etc. are provided on the crushed stone layer R1 depending on the purpose.

Next, the operation of the liquefaction prevention ground construction method using the drain material 1 of this embodiment will be explained.
The drain material 1 configured in this way includes a perforated pipe 2 placed at the center, a drainage sheet 3 formed of a highly rigid drainage material 31 wrapped around the perforated pipe 2, and a cylindrical sheet placed around the outer periphery of the perforated pipe 2. The outer peripheral filter 4 is provided.

For this reason, multiple drainage routes are formed by the perforated pipe 2 and the drainage sheet 3 wrapped around it, and the excess pore water pressure that occurs during large-scale earthquakes can be quickly removed using the large cross-section channel. It can be dissipated to prevent liquefaction.

In addition, since the perforated pipe 2 and the circulating drainage sheet 3 form the highly rigid drain material 1, the rigidity of the ground G will not be reduced even if a large number of drainage materials are buried. In other words, if a hollow drain material is used only to dissipate excess pore water pressure, many holes from which soil has been removed will be formed in the ground G, which may reduce rigidity and make the ground G more susceptible to deformation. There is. On the other hand, if the highly rigid drain material 1 is buried instead of the soil, the rigidity of the ground G can be maintained or increased, and the occurrence of ground deformation such as during a large-scale earthquake can be prevented.

Furthermore, if the drain material 1 is formed in a cylindrical shape, it can be efficiently pushed into the ground G with less resistance by attaching a conical anchor plate 5 to the tip. Therefore, it has excellent workability.

Further, by disposing a cylindrical outer peripheral filter 4 on the outer periphery of the roll-shaped drainage sheet 3, it is possible to prevent soil particles from entering the flow path of the drainage sheet 3, and to prevent the drainage of the drain material 1 in the vertical direction. It is possible to make the route less likely to become clogged.

In addition, when manufacturing the drainage sheet 3, which is made short and easy to transport, to be used as the drain material 1 at the installation site, the roll-shaped drainage sheet 3 is housed in the hollow part 41 of the cylindrical outer peripheral filter 4. If you go, you can easily assemble it.

Furthermore, the drainage sheets 3, . If so, each movement is restricted and the integrity of the drain material 1 can be maintained.

In addition, in the liquefaction countermeasure ground structure, by burying a plurality of drain materials 1,... in the ground G at intervals in the horizontal direction, the ground structure has excellent drainage performance without reducing the rigidity of the ground G. It can be done.

Also, between the upper ends of the perforated pipes 2, ... of the drain materials 1, ... arranged vertically at intervals in the horizontal direction, the perforated pipes of the horizontally drawn drain material 1A are connected in the horizontal direction. By connecting through 2A, the interstitial water collected by the drain material 1 can be quickly drained.

In the liquefaction countermeasure ground construction method of this embodiment, the drain material 1 is drawn in a bent state through the gap between the ground surface and the lower end opening of the mandrel 61, so that the drain material 1 becomes elongated. can also be easily inserted into the interior of the mandrel 61.

Further, by pushing the drain material 1 into the ground G while applying vibration (vibration) to the mandrel 61 using the vibrator 64, the density of the ground G can be increased during pouring. As a result, it is possible to reduce the amount of residual settlement that occurs after excessive pore water pressure dissipates.
Furthermore, by using not only vibration driving using a vibro but also high-pressure water injection using a water jet, the density increasing effect can be further enhanced. This density-increasing effect can be obtained by using only vibro casting, only water jet casting, or using a combination of casting methods. As a result, the undrained shear strength exerted during an earthquake can also be increased.

Hereinafter, Example 1 using a drain material 1B, which is a drain material for liquefaction prevention in a different form from the drain material 1 described in the above embodiment, will be described with reference to FIGS. 10 and 11. Note that the same terminology or the same reference numerals will be used to describe parts that are the same or equivalent to those described in the above embodiments.

In the embodiment described above, a case was explained in which a short drainage sheet 3 was used, but in this first embodiment, a case in which a longer drainage sheet 3B was used will be explained. This drainage sheet 3B is formed only from a plate-shaped highly rigid drainage material 31. That is, the shape-retaining sheet 32 described in the embodiment is not pasted.

As shown in FIG. 10, this drainage sheet 3B is formed in a medium-sized shape with a length of 1.5 m or more, for example, about 5 m to 7 m. Although it depends on the number of windings and the aspect ratio, if the length is around this extent, it can be bent when inserted into the mandrel 61.

Further, a shape retaining band 34 is used as a shape retaining portion that retains the shape of the wrapped drainage sheet 3B. The shape-retaining band 34 is made of a material such as a synthetic resin material such as plastic or geosynthetics, or a nonwoven fabric, and is formed into a band, string, or ring shape.

The shape retaining bands 34 are attached at intervals in the axial direction of the drainage sheet 3B wound up into a cylindrical shape. For example, they are arranged at intervals of about 50 cm to 100 cm. The drainage sheet 3B manufactured in this manner has the uneven surface portion 311 and the shape retaining band 34 exposed on the outer peripheral surface.

Therefore, as shown in FIG. 11, the drainage sheet 3B is housed in a cylindrical outer peripheral filter 4B. The outer circumferential filter 4B is made of water-permeable nonwoven fabric or the like and has approximately the same length as the drainage sheet 3B.

The drain material 1B of Example 1 can be formed by connecting one piece or a plurality of pieces. For purposes of explanation, the drain material placed on the upper side is referred to as upper drain material 1Ba, and the drain material placed on the lower side is referred to as lower drain material 1Bb.

A perforated pipe 2B of approximately the same length is inserted into the central hole of the drainage sheet 3B housed in the outer peripheral filter 4B. In short, the upper drain material 1Ba and the lower drain material 1Bb have all the unit length structures of the drain material 1B.

When connecting the upper drain material 1Ba and the lower drain material 1Bb, insert the lower end 23 of the perforated pipe 2B of the upper drain material 1Ba into the upper end 22 of the perforated pipe 2B of the lower drain material 1Bb, and The lower end 43 of the outer filter 4B of the upper drain material 1Ba is inserted into the opening of the upper end 42 of the outer filter 4B of the lower drain material 1Bb.

The upper edge of the upper end portion 42 of the outer filter 4B of the lower drain material 1Bb is joined to the outer circumferential surface of the outer filter 4B of the upper drain material 1Ba by providing a joint 44 by welding, adhesive, or the like.

Since the drain material 1B of Example 1 configured in this way does not have the shape-retaining sheet 32 bonded to it, the material cost can be reduced compared to the drain material 1 described in the above embodiment. For example, when using the shape-retaining band 34 made of the same material as the shape-retaining sheet 32, the amount used can be significantly reduced.

Further, by using the drainage sheet 3B which is longer than the drainage sheet 3 described in the embodiment, it is possible to reduce the effort required to manufacture the drain material 1B. Furthermore, by manufacturing unit length drain material (1Ba, 1Bb) containing the drainage sheet 3B and perforated pipe 2B in the hollow part 41 of the outer peripheral filter 4B at the factory, the lower drain material 1Bb By simply connecting the upper drain material 1Ba to the drain material 1Ba, the drain material 1B of a desired length can be manufactured in a short time.
Note that the other configurations and effects of Example 1 are substantially the same as those of the embodiment described above, and therefore description thereof will be omitted.

The embodiments and examples of the present invention have been described above in detail with reference to the drawings, but the specific configuration is not limited to these embodiments or examples, and may be modified without departing from the gist of the present invention. Modifications in design are included in the invention.

For example, in the first embodiment, the perforated pipe 2B having the same length as the drainage sheet 3B is used, but the invention is not limited to this. For example, a perforated pipe 2 having the same length as the drain material 1B to be buried is used, and a peripheral filter 4B containing a plurality of drainage sheets 3B is assembled to the long perforated pipe 2. I can go.

1, 1B: Drain material (drain material for liquefaction countermeasures)
1A: Horizontal drain material (drain material for liquefaction countermeasures)
1B: Drain material (drain material for liquefaction countermeasures)
2, 2A, 2B: Perforated pipes 3, 3B: Drainage sheet 31: Highly rigid drainage material 32: Shape retention sheet (shape retention part)
34: Shape retention band (shape retention part)
4, 4B: Periphery filter 5: Anchor plate (anchor part)
6, 6A: Casting machine 61: Mandrel 64: Vibrator 64a: Vibration 65: Jet section 65a: High pressure water G: Ground

Claims (6)

A perforated pipe arranged at the center, a drainage sheet formed of a highly rigid geosynthetic drainage material with an embossed structure wrapped around the perforated pipe, and a cylindrical drainage sheet arranged around the outer periphery of the wrapped drainage sheet. A construction method for a liquefaction prevention ground using a liquefaction prevention drain material equipped with a peripheral filter, the method comprising:
A step of drawing the liquefaction prevention drain material, which has a conical anchor portion attached to the tip, into the interior of a mandrel attached to a casting machine from the lower end opening of the mandrel;
pushing the liquefaction countermeasure drain material into the ground together with the mandrel;
and pulling out the mandrel after the anchor portion reaches a predetermined depth,
In the step of drawing the liquefaction countermeasure drain material from the lower end opening of the mandrel, the lower end of the wire rope passed through the inner space of the mandrel is connected to the end of the perforated pipe of the liquefaction countermeasure drain material. . A method for constructing a liquefaction countermeasure ground, characterized in that the liquefaction countermeasure drain material in a bent state is drawn through a gap between the ground surface and the lower end opening by winding up the wire rope. The casting machine has at least one of a vibrator and a high-pressure water jet section,
Claim characterized in that the step of pushing the liquefaction countermeasure drain material into the ground is performed while at least one of applying vibration to the mandrel by the vibrator and jetting high-pressure water from the jet part. 1. The construction method for the liquefaction prevention ground according to 1. 3. The method of constructing a liquefaction prevention ground according to claim 1, wherein the drainage sheet has a shape retained by a shape retention band. The method for constructing a liquefaction prevention ground according to any one of claims 1 to 3, further comprising a water-permeable shape-retaining sheet formed in a laminated structure with the highly rigid geosynthetic drainage material. 5. The liquefaction prevention ground construction method according to claim 1, wherein the drainage sheet is wrapped around two to four times. The method for constructing a liquefaction prevention ground according to any one of claims 1 to 5, wherein a plurality of the drainage sheets shorter than the long perforated pipe are arranged.