Construction method for liquefaction prevention ground

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

[Technical field]

[0001] The present invention relates to a method for constructing a liquefaction countermeasure ground using a liquefaction countermeasure drain material that is buried in the ground as a liquefaction countermeasure. [Background technology]

[0002] In order to prevent ground liquefaction during a large earthquake, a construction method is known in which drainage material with high drainage performance is poured at specified intervals into ground that may be subject to liquefaction (see Patent Documents 1-3, etc.).

[0003] In the liquefaction countermeasures methods disclosed in Patent Documents 1 to 3, synthetic resin drainage material is buried vertically in the ground, and liquefaction is prevented by quickly dissipating excess pore water pressure generated during an earthquake using the drainage material.

[0004] For example, in Patent Document 1, a large number of vertically oriented cylindrical drainage materials are arranged at intervals in the horizontal direction to provide liquefaction countermeasures for a construction area that spreads over a wide area. The cylindrical drainage materials used include synthetic resin filter material formed into a cylindrical shape, and hollow pipes such as polyvinyl chloride pipes with many water permeable holes drilled in the peripheral wall.

[0005] In addition, the drainage material disclosed in Patent Document 2 is made of semi-rigid polyvinyl chloride resin or the like and is molded into a hollow rectangular cross-section, and since it cannot be wound into a roll, it is buried to a specified depth in fixed lengths that can be transported by truck, and then connected together at the construction site using connectors.

[0006] On the other hand, in the liquefaction countermeasure method described in Patent Document 3, permeable vanes made of strip-shaped synthetic resin plates covered with a covering material such as netting are connected together (for example, four sheets) to form a cross shape when viewed in a plan view, and then pressed into the ground where liquefaction countermeasures are required. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2015-169045 A [Patent Document 2] JP 2012-241385 A [Patent Document 3] Patent No. 2743031 Summary of the Invention [Problem to be solved by the invention]

[0008] However, casting a large number of hollow drainage materials into the ground carries the risk of reducing the rigidity of the ground throughout the entire casting area. Even if it is possible to dissipate excess pore water pressure in the event of a large earthquake, there is the issue that ground deformation will occur due to the reduced rigidity.

[0009] In addition, rectangular cross-section drainage material such as that disclosed in Patent Document 2 is hard and cannot be rolled up, which increases transportation costs, makes connection work time-consuming, and makes it difficult to bury in the ground due to the high resistance of the rectangular cross-section, posing construction issues.

[0010] Therefore, an object of the present invention is to provide a method for implementing liquefaction countermeasures without reducing the rigidity of the ground and for implementing liquefaction countermeasures with excellent workability. [Means for solving the problem]

[0011] In order to achieve the above-mentioned objective, the construction method for liquefaction countermeasure ground of the present invention uses a liquefaction countermeasure drainage material that is buried in the ground as a liquefaction countermeasure, the liquefaction countermeasure drainage material comprising a perforated pipe placed in the center, a drainage sheet formed from a high-rigidity geosynthetics drainage material with an embossed structure that is wrapped around the perforated pipe, and a cylindrical peripheral filter placed on the outer periphery of the wrapped drainage sheet.

[0012] The method includes the steps of: drawing the liquefaction countermeasure drain material, which has a conical anchor portion attached to its tip, into the inner space of a mandrel attached to a casting machine through 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 has reached a predetermined depth. In the step of drawing the liquefaction countermeasure drain material from the lower end opening of the mandrel, a lower end of a 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, and the wire rope is wound up to draw the liquefaction countermeasure drain material in a bent state through the gap between the ground surface and the lower end opening.

[0013] Here, the driving machine has at least one of a vibrator and a high-pressure water jet section, and the process of pushing the liquefaction countermeasure drainage material into the ground can be performed while at least one of imparting vibrations to the mandrel with the vibrator and spraying high-pressure water from the jet section.

[0014] The drainage sheet may be configured such that the wrapped shape is maintained by a shape-retaining band. Furthermore, the drainage sheet may have a water-permeable shape-retaining sheet formed in a laminated structure with the high-rigidity geosynthetics drainage material.

[0015] The drainage sheet may be wound around the perforated pipe two to four times. Furthermore, a plurality of drainage sheets each shorter than the long perforated pipe may be disposed around the long perforated pipe. Effect of the Invention

[0016] The liquefaction countermeasure drainage material used in the present invention, configured in this manner, comprises a perforated pipe placed in the center, a drainage sheet formed from high-rigidity drainage material wrapped around the pipe, and a cylindrical peripheral filter placed on the outer periphery of the pipe.

[0017] Therefore, the perforated pipe and the drainage sheet wrapped around it form multiple drainage paths, quickly dissipating excess pore water pressure and preventing liquefaction. In addition, the perforated pipe and the surrounding drainage sheet form a highly rigid drainage material, so even if a large number of them are buried, the rigidity of the ground is not reduced.

[0018] Furthermore, if the drainage material is formed in a cylindrical shape, it is easy to cast and has excellent workability. Also, since a cylindrical peripheral filter is arranged on the outer periphery of the wrapped drainage sheet, clogging of the drainage path of the drainage material can be prevented.

[0019] Furthermore, even when the drainage sheet is made short to make it easier to transport or to make it easier to bend as a drainage material, if it is contained within a cylindrical outer peripheral filter, it can maintain its integrity as a drainage material even during work at the pouring site.

[0020] By burying such liquefaction countermeasure drain materials in the ground at intervals in the horizontal direction, it is possible to create a liquefaction countermeasure ground structure that does not reduce the rigidity of the ground. In addition, by connecting the upper ends of the perforated pipes of the liquefaction countermeasure drain materials arranged at intervals in the horizontal direction with perforated pipes of the drain materials oriented horizontally, the collected pore water can be quickly drained.

[0021] In the invention of the construction method for liquefaction countermeasure ground, when the liquefaction countermeasure drain material is forced into the ground while vibrating the mandrel with a vibrator or by spraying high-pressure water from the jet section, the density of the ground can be increased during casting, and the amount of residual settlement after dissipation of excess pore water pressure can be reduced. Furthermore, by drawing the liquefaction countermeasure drain material in a bent state through the gap between the ground surface and the lower end opening of the mandrel, even if the liquefaction countermeasure drain material is long, it can be easily inserted into the inner space of the mandrel. [Brief description of the drawings]

[0022] [Figure 1]1 is a perspective view illustrating the configuration of a liquefaction countermeasure ground structure in which a drainage material according to an embodiment of the present invention is buried. FIG. [Diagram 2] FIG. 2 is a perspective view illustrating the configuration of a drain material according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a process diagram illustrating a method for producing a drainage sheet. [Figure 4] FIG. 2(a) is an explanatory diagram showing the packaging of the drainage sheet, and FIG. 2(b) is an explanatory diagram showing the appearance of the peripheral filter. [Diagram 5] FIG. 1 is a process diagram illustrating a method for manufacturing a drain material. [Figure 6] This is a process diagram explaining the work of setting drainage material in a concrete pouring machine. [Figure 7] This is a process diagram explaining the work of pouring drainage material into the ground. [Figure 8] FIG. 1 is a diagram conceptually explaining the density increasing effect of vibration pouring and high-pressure water injection. [Figure 9] 1 is a cross-sectional view illustrating a configuration in which a horizontal drain material is connected to a vertically buried drain material. FIG. [Figure 10] FIG. 2 is a perspective view illustrating the configuration of the drainage sheet of the first embodiment. [Figure 11] FIG. 2 is a perspective view illustrating the configuration of the drain material of the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram for explaining the configuration of a liquefaction countermeasure ground structure in which a drainage material 1, which is a liquefaction countermeasure drainage material of this embodiment, is buried, and Fig. 2 is a perspective view for explaining the configuration of the drainage material 1 in detail.

[0024] The drain material 1 of this embodiment is buried in the ground G as a measure against liquefaction. That is, the drain material 1 is pushed vertically into the ground G (see FIG. 7), and is arranged in large numbers in the construction area at intervals in the horizontal direction.

[0025] Here, the length of the drain material 1 is set according to the depth of the liquefaction layer of the liquefaction countermeasure ground. Also, the horizontal 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.

[0026] As shown in Figure 2, the drainage material 1 of this embodiment is mainly composed of a perforated pipe 2 placed in the center, a drainage sheet 3 wrapped around the perforated pipe 2, and a cylindrical peripheral filter 4 placed on the outer periphery of the wrapped drainage sheet 3.

[0027] The perforated pipe 2 is a flexible cylindrical pipe material made of synthetic resin material (geosynthetics) or the like. For example, a long, flexible pipe material such as a CD pipe can be used. The cylindrical pipe material is formed into a perforated pipe 2 by drilling a large number of holes in its peripheral wall. For example, a perforated pipe 2 with a diameter of about 3 cm can be used.

[0028] On the other hand, as shown in Fig. 3, the drainage sheet 3 is formed in a laminated structure of a plate-shaped high-rigidity drainage material 31 and a water-permeable shape-retaining sheet 32. The high-rigidity drainage material 31 is a sheet-shaped member (high-rigidity geosynthetic drainage material) in which highly rigid geosynthetics is molded into an uneven surface portion 311, as shown in an enlarged view on the left side of Fig. 3.

[0029] High-rigidity drainage material 31 formed with an embossed structure such as uneven surface portion 311 made of hard synthetic resin material or the like has flow paths formed in various in-plane directions. High-rigidity drainage material 31 also has a plurality of water-passing holes 312, ... drilled through the surface material from front to back. Groundwater or the like can pass through these water-passing holes 312.

[0030] A shape-retaining sheet 32 ​​having the same size as the rectangular high-rigidity drainage material 31 in a plan view is attached to the high-rigidity drainage material 31. Therefore, the flow paths of the high-rigidity drainage material 31 are flow paths along the shape-retaining sheet 32.

[0031] The shape-retaining sheet 32 ​​is a shape-retaining part that is attached to retain the shape of the high-rigidity drainage material 31. That is, as shown in the right end of Fig. 3, the shape-retaining sheet 32 ​​is attached to form a laminated structure so that the high-rigidity drainage material 31 does not bend when the drainage sheet 3 is stood vertically. In addition, by laminating the shape-retaining sheets 32, it becomes easier to retain the shape of the wrapped drainage sheet 3. For such a shape-retaining sheet 32, a material that is expected to also function as a filter, such as a nonwoven fabric, can be used.

[0032] In Fig. 3, a rectangular drainage sheet 3 with a vertical length of 1 m is shown, but this is not limited to this and any length can be used. When using a short drainage sheet 3 as described later, a length of about 1.0 m to 1.5 m can be used.

[0033] During production, such a strip-shaped drainage sheet 3 is wound around a cylindrical core material 33. The number of times the drainage sheet 3 is wound can be set arbitrarily between 2 and 4 turns. Figure 4(a) shows the packaged state of the drainage sheet 3 wound three times with the central core material 33 removed.

[0034] 4(b) shows the external appearance of a cylindrical peripheral filter 4 in which a cylindrically shaped drainage sheet 3 is housed in a hollow portion 41. The peripheral filter 4 can be made of a water-permeable nonwoven fabric or the like. The peripheral filter 4 can also be in the form of a bag with a bottom.

[0035] The peripheral filter 4 is formed to a continuous length approximately equal to the length of the drain material 1 buried in the ground G. In Fig. 4(b), a peripheral filter 4 having a length of 10 m is shown, but the present invention is not limited to this and the peripheral filter 4 is formed to a required designed length. The diameter of the peripheral filter 4 is also not limited to 0.1 m and can be set arbitrarily, for example, from about 0.09 m to 0.11 m.

[0036] As shown in Fig. 2, the peripheral filter 4 forms the peripheral surface of the drainage material 1. The drainage sheet 3, which is wound up about two to four times and housed in the peripheral filter 4, and the perforated pipe 2 form two vertical drainage paths.

[0037] In short, when an earthquake causes excess pore water pressure around the drain material 1, pore water permeates from the peripheral filter 4 toward the drainage sheet 3, and water moves between the surrounding drainage sheets 3 through the water passage holes 312. Then, the flow paths of the drainage sheets 3 formed along the shape-retaining sheet 32 ​​perform vertical drainage treatment.

[0038] Furthermore, the pore water that has flowed into the drainage sheet 3 flows in through the lower opening of the perforated pipe 2 and rises up the perforated pipe 2 for vertical drainage treatment. It may also flow into the pipe through holes in the peripheral wall of the perforated pipe 2 adjacent to the drainage sheet 3 and be drained by the perforated pipe 2. In this way, by performing drainage treatment through two drainage paths with wide cross sections, excess pore water pressure can be quickly dissipated.

[0039] Furthermore, by providing two drainage paths, the diameter of the perforated pipe 2 can be made smaller than when only a conventional cylindrical drain material is used. For example, if a conventional cylindrical drain material needs to have a diameter of about 8 cm, the diameter of the perforated pipe 2 can be made smaller to about 3 cm.

[0040] Furthermore, since the surrounding drainage sheet 3 is formed from a high-rigidity drainage material 31, the drainage material 1 composed of a perforated pipe 2 having a relatively small diameter and a highly rigid drainage sheet 3 does not lose its rigidity even when placed in place to replace the soil of the ground G.

[0041] Next, a method for producing the drainage material 1 of this embodiment will be described with reference to Figs. 4 and 5. First, a plurality of short rolled drainage sheets 3 are produced. The drainage sheets 3 can be produced by wrapping the drainage sheet 3 in an unfolded state as shown in the center of Fig. 3 around a core material 33 having the same outer diameter as the perforated pipe 2 a predetermined number of times (e.g., three times).

[0042] The edges of the shape-retaining sheet 32 ​​of the rolled up drainage sheet 3 are joined with an adhesive or the like to prevent it from unfolding, and the core material 33 is removed. The rolled up drainage sheet 3 is packaged in a short cylindrical shape with a height of about 1.0 m to 1.5 m, so it can be efficiently transported to the casting site by truck or the like.

[0043] On the other hand, the cylindrical peripheral filter 4 is long, but since it is made of nonwoven fabric or the like and can be rolled up or folded, it can be efficiently transported to the casting site by truck, etc. In addition, the perforated pipe 2, which is about the same length as the peripheral filter 4, is also flexible, so it can be transported to the casting site in a rolled up state.

[0044] Next, at the casting site, as shown in Fig. 5(a), the tip of the perforated pipe 2 is attached to a cone-shaped anchor plate 5 formed of a steel plate or the like that serves as the anchor part. Then, the peripheral filter 4 is placed so as to cover the periphery of the perforated pipe 2, and the tip of the peripheral filter 4 is joined to the anchor plate 5 with an adhesive or the like.

[0045] As shown in Fig. 5(b), a short roll of drainage sheet 3 transported to the casting site is inserted into the hollow portion 41 of the peripheral filter 4 with the perforated pipe 2 disposed at the center. The perforated pipe 2 is passed through the hole in the center of the roll, and the drainage sheet 3 is moved to the position of the anchor plate 5.

[0046] In the same manner, short drainage sheets 3 are successively inserted into the hollow portion 41 of the peripheral filter 4, and the drainage sheets 3 are lined up in order from the anchor plate 5 side, as shown in Fig. 5(c). This operation is continued until the hollow portion 41 of the peripheral filter 4 is filled with the drainage sheets 3, as shown in Fig. 5(d).

[0047] Next, with reference to Figures 6 to 8, a construction method for liquefaction countermeasure ground according to this embodiment will be described, in which the manufactured drainage material 1 is cast into the ground G. A casting machine 6, 6A as shown in Figure 6 or Figure 8 is used to cast the drainage material 1, but since this is a known machine, a brief description will be given.

[0048] The concrete pouring machine 6 shown in Fig. 6(a) is movable by crawlers and includes a leader 62 and a slider 621 that can rise and fall along the leader 62. The leader 62 can be raised vertically, and the mandrel 61 is supported by the slider 621.

[0049] The mandrel 61 is a cylindrical rod pipe with an inner diameter slightly larger than the outer diameter of the drainage material 1, and a wire rope 63 suspended from the upper end of a leader 62 is passed through the inner space. The lower end of the wire rope 63 is connected to the end of the perforated pipe 2 of the drainage material 1 that has been brought to the casting site.

[0050] When inserting the drain material 1 into the mandrel 61, first, the mandrel 61 is pulled up so that there is a gap of about 1 m between it and the ground surface. Next, the wire rope 63 is wound up, and the upper part of the drain material 1 is pulled into the lower end opening of the mandrel 61, as shown in FIG. 6(b).

[0051] Here, since the drain material 1 is composed of the flexible perforated pipe 2, the peripheral filter 4, and a plurality of short drainage sheets 3, ..., it can be pulled in a bent state when inserted into the mandrel 61. In other words, even if each of the drainage sheets 3 is hard and does not bend, it can be bent in the gaps between the drainage sheets 3, 3.

[0052] The anchor plate 5 attached to the tip of the drain material 1 is formed so that the maximum diameter part of the cone is larger than the inner diameter of the mandrel 61, so that the anchor plate 5 gets caught on the lower end of the mandrel 61, stopping the insertion of the drain material 1 into the mandrel 61.

[0053] 7, the anchor plate 5 is driven into the ground G, and the mandrel 61 is pushed down by the slider 621, so that the drain material 1 together with the mandrel 61 is pushed 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 together with the mandrel 61 is pushed down.

[0054] Here, when using a concrete pouring machine 6A equipped with a vibrator 64 and a jet section 65 as shown in FIG. 8, vibrations 64a can be applied to the ground G by the vibrator 64 when the mandrel 61 is pushed into the ground G.

[0055] When vibrating (vibration 64a) is applied to ground G, if the ground G is a saturated, loose sand layer, the soil particles will settle as if falling into water, the sedimentary structure will be reconstructed, and the density will increase, thereby increasing the undrained strength of ground G to resist liquefaction.

[0056] Furthermore, high-pressure water 65a can be jetted from a jet unit 65 provided at the tip of the mandrel 61. Also, only the jet unit 65 can jet the high-pressure water 65a.

[0057] When vibration compaction is performed in this way using a vibro or water jet (high-pressure water injection), a volume change (volume reduction G1) occurs in ground G, as shown in the lower part of Figure 8, and the density of ground G increases, resulting in a ground structure that can suppress residual settlement.

[0058] The mandrel 61 is pushed into the ground G until the anchor plate 5 reaches a predetermined depth determined by design, etc. After the drain material 1 is pushed into the ground G in this manner, the slider 621 is raised to pull out only the mandrel 61 from the ground G.

[0059] When the mandrel 61 is pulled out, the drainage material 1 with the anchor plate 5 attached to its tip is buried vertically in the ground G, as shown in the right side of Fig. 7. Fig. 1 shows the state after construction in which the drainage material 1, ... is repeatedly poured while the pouring machine 6 (6A) is moved laterally.

[0060] The upper ends of the drainage materials 1 protruding from the ground G where liquefaction countermeasure work has been carried out are connected by a horizontal pipe (not shown) or the like. In other words, the water that rises up the perforated pipe 2 is quickly drained through the horizontal pipe.

[0061] On the other hand, as shown in Fig. 9, a horizontal drain material 1A, which is a drain material for liquefaction countermeasures having the same structure as the drain material 1, can be used as a horizontal pipe. The horizontal drain material 1A is arranged, for example, in a horizontal direction in order to connect the upper ends of the drain materials 1 that are cast vertically so that water can pass through them.

[0062] 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 has a diameter of about 150 mm.

[0063] 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 joint material 21 such as a T-shaped, L-shaped, or cross-shaped joint material. Single-grain crushed stone or the like is filled around the horizontal drain material 1A arranged in this way to form a crushed stone layer R1 with a thickness of about 300 mm. In addition, a roadbed layer R2, an asphalt layer R3, or the like is provided on the crushed stone layer R1 depending on the application.

[0064] Next, the operation of the method for constructing liquefaction-resistant ground using the drainage material 1 of this embodiment will be described. The drainage material 1 constructed in this manner comprises a perforated pipe 2 placed in the center, a drainage sheet 3 formed from a high-rigidity drainage material 31 wrapped around the perforated pipe, and a cylindrical peripheral filter 4 placed on the outer periphery of the perforated pipe.

[0065] As a result, the perforated pipe 2 and the drainage sheet 3 wrapped around it form multiple drainage paths, allowing excess pore water pressure that occurs during a large-scale earthquake to be quickly dissipated in the large cross-sectional flow path, preventing liquefaction.

[0066] Furthermore, the perforated pipe 2 and the surrounding drainage sheet 3 form a highly rigid drainage material 1, so even if many are buried, the rigidity of the ground G is not reduced. In other words, with a hollow drainage material that is only used to dissipate excess pore water pressure, many holes are formed in the ground G from which the soil has been removed, which reduces the rigidity and may make the ground G more susceptible to deformation. In contrast, if the highly rigid drainage material 1 is buried instead of the soil, the rigidity of the ground G is maintained or increased, making it possible to prevent ground deformation during large-scale earthquakes and the like.

[0067] Furthermore, if the drain material 1 is formed in a cylindrical shape, it can be efficiently pushed into the ground G with little resistance by attaching a cone-shaped anchor plate 5 to the tip. Therefore, it has excellent workability.

[0068] In addition, by placing a cylindrical peripheral filter 4 on the outer periphery of the roll-shaped drainage sheet 3, soil particles can be prevented from entering the flow path of the drainage sheet 3, making it less likely that the vertical drainage path of the drain material 1 will become clogged.

[0069] Furthermore, when producing the drainage sheet 3 in a short length for ease of transport at the construction site to be used as the drainage material 1, if the roll-shaped drainage sheet 3 is placed in the hollow portion 41 of the cylindrical outer peripheral filter 4, assembly work can be easily performed.

[0070] Furthermore, at the casting site, even during operations such as transporting the sheets or bending them when inserting them into the inner space of the mandrel 61, if the drainage sheets 3,... are contained in the hollow portion 41 of the cylindrical outer peripheral filter 4, the movement of each sheet is restricted and the integrity of the drainage material 1 can be maintained.

[0071] In addition, in a liquefaction countermeasure ground structure, by burying multiple drainage materials 1,... in the ground G at intervals in the horizontal direction, a ground structure with excellent drainage performance can be created without reducing the rigidity of the ground G.

[0072] In addition, by connecting the upper ends of the perforated pipes 2, ... of the drain materials 1, ... that are arranged vertically and spaced apart horizontally with a perforated pipe 2A of the horizontally-oriented drain material 1A, the interstitial water collected by the drain material 1 can be quickly drained.

[0073] In the construction method for liquefaction-resistant ground in this embodiment, the drainage material 1 in a bent state is pulled through the gap between the ground surface and the lower end opening of the mandrel 61, so that even if the drainage material 1 becomes long, it can be easily inserted into the inner space of the mandrel 61.

[0074] In addition, by forcing the drain material 1 into the ground G while applying vibration (vibro) to the mandrel 61 by the vibrator 64, the density of the ground G can be increased during casting. As a result, the amount of residual settlement that occurs after the dissipation of excess pore water pressure can be reduced. Furthermore, by using not only vibro vibration pouring but also high-pressure water jets, the density increase effect can be further enhanced. This density increase effect can be obtained by any pouring method, vibro only, water jet only, or both. As a result, the undrained shear strength exerted during an earthquake can also be increased. EXAMPLES

[0075] Hereinafter, Example 1 using drain material 1B, which is a liquefaction countermeasure drain material having a different form from the drain material 1 described in the above embodiment, will be described with reference to Figures 10 and 11. Note that the same terms or the same reference numerals will be used to describe the same or equivalent parts as those described in the above embodiment.

[0076] In the above embodiment, the case where a short drainage sheet 3 is used is described, but in this Example 1, the case where a longer drainage sheet 3B is used is described. This drainage sheet 3B is formed only by a plate-shaped high-rigidity drainage material 31. In other words, the shape-retaining sheet 32 ​​described in the above embodiment is not attached.

[0077] 10, the drainage sheet 3B is formed into a medium length of 1.5 m or more, for example, about 5 m to 7 m. Although it depends on the number of turns and the aspect ratio, if it is of this length, it can be bent when inserted into the mandrel 61.

[0078] A shape-retaining band 34 is used as a shape-retaining part for retaining 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 in a belt-like, string-like, or ring-like shape.

[0079] The shape-retaining bands 34 are attached at intervals in the axial direction of the cylindrically wound drainage sheet 3B. For example, they are arranged at intervals of about 50 cm to 100 cm. The drainage sheet 3B thus manufactured has the uneven surface portion 311 and the shape-retaining bands 34 exposed on the outer peripheral surface.

[0080] Therefore, as shown in Fig. 11, the drainage sheet 3B is housed in a cylindrical peripheral filter 4B. This peripheral filter 4B is made of a water-permeable nonwoven fabric or the like and is formed to have approximately the same length as the drainage sheet 3B.

[0081] The drain material 1B of the first embodiment can be formed by connecting one piece or a plurality of pieces. For the sake of explanation, the drain material arranged on the upper side is referred to as an upper drain material 1Ba, and the drain material arranged on the lower side is referred to as a lower drain material 1Bb.

[0082] A perforated pipe 2B of approximately the same length is inserted into the central hole of the drainage sheet 3B housed in the peripheral filter 4B. In short, the upper drain material 1Ba and the lower drain material 1Bb have all the configurations of the unit length of the drainage material 1B.

[0083] When connecting the upper drain material 1Ba and the lower drain material 1Bb, the lower end 23 of the perforated pipe 2B of the upper drain material 1Ba is inserted into the upper end 22 of the perforated pipe 2B of the lower drain material 1Bb, and the lower end 43 of the peripheral filter 4B of the upper drain material 1Ba is inserted into the opening of the upper end 42 of the peripheral filter 4B of the lower drain material 1Bb.

[0084] The upper edge of the upper end portion 42 of the peripheral filter 4B of the lower drain material 1Bb is joined to the outer peripheral surface of the peripheral filter 4B of the upper drain material 1Ba by providing a joint 44 by welding, adhesive or the like.

[0085] The drainage material 1B of Example 1 configured as above can reduce material costs compared to the drainage material 1 described in the above embodiment because it does not have the shape-retaining sheet 32 ​​attached. For example, when using a shape-retaining band 34 made of the same material as the shape-retaining sheet 32, the amount of material used can be significantly reduced.

[0086] In addition, by using a drainage sheet 3B that is longer than the drainage sheet 3 described in the above embodiment, the labor required to manufacture the drainage material 1B can be reduced. Furthermore, by manufacturing unit-length drainage materials (1Ba, 1Bb) in which the drainage sheet 3B and the perforated pipe 2B are housed in the hollow portion 41 of the peripheral filter 4B at the factory, the drainage material 1B of the desired length can be manufactured in a short time at the casting site simply by connecting the upper drainage material 1Ba to the lower drainage material 1Bb. Other configurations and effects of the first embodiment are substantially the same as those of the above-described embodiment, and therefore description thereof will be omitted.

[0087] Although the embodiment and examples of the present invention have been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment or example, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0088] For example, in the first embodiment, the case where the perforated pipe 2B is used that is approximately the same length as the drainage sheet 3B is described, but the present invention is not limited to this. For example, it is also possible to use a perforated pipe 2 that is approximately the same length as the buried drain material 1B, and to assemble the peripheral filter 4B that contains a plurality of drainage sheets 3B to the long perforated pipe 2. [Explanation of symbols]

[0089] 1, 1B: Drainage material (drainage material for liquefaction countermeasures) 1A: Horizontal drainage material (drainage material for liquefaction countermeasures) 1B: Drainage material (drainage material for liquefaction countermeasures) 2,2A,2B: Perforated pipe 3, 3B: Drainage sheet 31: High rigidity drainage material 32: Shape retention sheet (shape retention part) 34: Shape retention band (shape retention part) 4,4B: Peripheral filter 5: Anchor plate (anchor part) 6,6A:Pouring machine 61: Mandrel 64: Vibrator 64a: Vibration 65: Jet Club 65a: High pressure water G: Ground

Claims

1. A construction method for liquefaction countermeasure ground using a liquefaction countermeasure drain material comprising a perforated pipe arranged at the center, a drainage sheet formed of a high-rigidity geosynthetic drainage material with an embossed structure wrapped around the perforated pipe, and a cylindrical peripheral filter arranged on the outer periphery of the wrapped drainage sheet, A step of drawing the liquefaction countermeasure drainage material having a conical anchor portion attached to a tip into an inner space of a mandrel attached to a concrete pouring machine from a lower end opening of the mandrel; pushing the liquefaction countermeasure drain material into the ground together with the mandrel; and withdrawing the mandrel after the anchor portion reaches a predetermined depth. The drainage material for liquefaction countermeasures is configured such that a plurality of drainage sheets each shorter than the long perforated pipe are arranged around the long perforated pipe, and the drainage sheet is formed to have an inner diameter slightly smaller than the inner diameter of the mandrel, so that the drainage sheet directly contacts the ground after the mandrel is pulled out, and The process of drawing in the liquefaction countermeasure drainage material from the lower end opening of the mandrel involves connecting the lower end of a wire rope passed through the inner space of the mandrel which is raised vertically to the end of the perforated pipe of the liquefaction countermeasure drainage material, and winding up the wire rope to draw in the liquefaction countermeasure drainage material in a bent state from a gap of approximately 1 m between the ground surface and the lower end opening, in a construction method for liquefaction countermeasure ground.

2. The concrete pouring machine has at least one of a vibrator and a high-pressure water jet unit, The construction method for liquefaction countermeasure ground as described in claim 1, characterized in that the process of pushing the liquefaction countermeasure drainage material into the ground is carried out while at least one of vibrating the mandrel with the vibrator and spraying high-pressure water from the jet section.

3. 3. The method for constructing liquefaction-prevention ground according to claim 1 or 2, characterized in that the shape of the drainage sheet wrapped around it is maintained by a shape-retaining band.

4. The construction method for 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 high-rigidity geosynthetics drainage material.

5. 5. The method for constructing liquefaction-prevention ground according to claim 1, wherein the drainage sheet is wrapped around the ground in two to four turns.

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