Improved ground and construction method therefor

Abstract

To provide an improved ground and a construction method therefor that can quickly discharge water content oozing out from an excavated in-situ ground due to liquefaction to a drainage ditch, and reduce damage such as subsidence, uplift, or the like of the ground surface.SOLUTION: An improved ground 10 comprises glass granulated sand 2 buried on an excavated in-situ ground 1 and in a recessed groove part 11 formed in the in-situ ground, a water permeable pipe 3 surrounded by the glass granulated sand and formed to be capable of communicating with a drainage ditch HK formed at an outer edge portion 12 of the in-situ ground, a waterproof sheet member 4 horizontally covering an upper surface of the glass granulated sand above the water permeable pipe, and a covering soil 5 laid above the waterproof sheet member.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to improved ground and a construction method thereof, and more particularly to improved ground for improving the foundation of a road or the like built on soft ground that is predicted to liquefy in an earthquake or the like, and a construction method thereof. [Background technology]

[0002] Generally, sandy ground is prone to liquefaction due to excessive pore water pressure generated within the ground during an earthquake. Structures such as roads built on this soft ground that is prone to liquefaction are likely to suffer damage such as subsidence or floating due to ground liquefaction. To prevent this damage, for example, Patent Document 1 discloses improved ground and its construction method.

[0003] The improved ground disclosed in Patent Document 1 is, for example, as shown in Figure 9, an improved ground 100 formed by laying a horizontal drainage waterproof sheet 103 over an underground conduit 102 buried along at least the outer edge of an excavated existing ground 101, the sheet having a composition and structure that can horizontally guide and drain water that springs up due to liquefaction and can suppress the uplift of soil and sand, and then forming cover soil 107 on the horizontal drainage waterproof sheet 103, with a water-permeable crack-preventing geotextile 106 interposed between a lower cover soil layer 104 and an upper cover soil layer 105. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-79550 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the improved ground 100 disclosed in Patent Document 1 has the following problems: Since the horizontal drainage waterproof sheet 103 is laid across the top of the culvert 102 buried along at least the outer edge of the excavated existing ground 101, it is possible for the horizontal drainage waterproof sheet 103 to prevent water gushing out from the existing ground 101 due to liquefaction from gush-out upward, but there is a problem in that it is difficult to quickly drain water accumulated between the existing ground 101 and the underside of the horizontal drainage waterproof sheet 103 into the culvert 102.

[0006] The present invention has been made to solve the above problems, and its purpose is to provide improved ground and its construction method that can quickly drain water that springs up from excavated ground due to liquefaction into a drainage ditch, thereby reducing damage such as subsidence and floating of the ground. [Means for solving the problem]

[0007] In order to solve the above problems, the improved ground and construction method of the present invention have the following configurations. (1) The improved ground of the present invention comprises glass granulated sand buried on top of an excavated existing ground and in a groove formed in the existing ground, a permeable pipe surrounded by the glass granulated sand and formed so as to be able to communicate with a drainage ditch formed on the outer edge of the existing ground, a waterproof sheet member horizontally covering the upper surface of the glass granulated sand above the permeable pipe, and cover soil laid above the waterproof sheet member. Here, glass granulated sand means glass sand formed into granules by crushing waste glass.

[0008] In this invention, the waterproof sheet member horizontally covers the upper surface of the glass granulated sand surrounding the permeable pipe and the upper surface of the glass granulated sand on the in-situ ground above the permeable pipe, which is formed to be able to communicate with a drainage ditch formed at the outer edge of the in-situ ground. This prevents water from liquefying the in-situ ground during an earthquake from gushing upward. Furthermore, water that accumulates on the underside of the waterproof sheet member can be quickly guided through the glass granulated sand into the permeable pipe and discharged from the permeable pipe into the drainage ditch. Furthermore, because glass granulated sand does not contain a large amount of silt or clay like pit sand, it has excellent permeability and is less likely to clog the permeable pipe. Therefore, water that liquefies the excavated in-situ ground can be quickly guided through the glass granulated sand into the permeable pipe. As a result, the possibility of damage such as ground subsidence or floating caused by liquefaction of the in-situ ground is reduced.

[0009] Therefore, according to the present invention, improved ground can be provided that can quickly drain water that springs up from the excavated ground due to liquefaction into a drainage ditch, thereby reducing damage such as subsidence and floating of the ground.

[0010] (2) In the improved ground described in (1), It is preferable that a water-permeable sheet member be provided between the waterproof sheet member and the glass granulated sand, joined to the underside of the waterproof sheet member and arranged horizontally.

[0011] In this invention, a water-permeable sheet member is provided between the waterproof sheet member and the glass granulated sand, and is joined to the underside of the waterproof sheet member and arranged horizontally. This allows moisture that accumulates on the underside of the waterproof sheet member to be guided through the water-permeable sheet member and the glass granulated sand into the water-permeable pipe, and then discharged from the water-permeable pipe into the drainage ditch. This means that moisture that springs up from the excavated ground due to liquefaction can be more quickly discharged into the drainage ditch.

[0012] (3) In the improved ground described in (1) or (2), The particle size distribution of the glass granulated sand is preferably such that particles with a particle size of less than 1.0 mm account for 30±5% of the total, with the remainder having a particle size of 1.0 mm or more and 5.0 mm or less. Here, particle size refers to the maximum dimension of the external shape of a single piece of glass granulated sand.

[0013] In the present invention, 30±5% of the glass granulated sand has a particle size of less than 1.0 mm, with the remainder having a particle size of 1.0 mm or more and 5.0 mm or less, thereby achieving both permeability and compactibility. That is, since 65-75% of the sand has a particle size of 1.0 mm or more and 5.0 mm or less, permeability is improved. Furthermore, since 30±5% of the sand has a particle size of less than 1.0 mm, particles with a particle size of less than 1.0 mm can fill the gaps between particles with a particle size of 1.0 mm or more and 5.0 mm or less, improving compactibility.

[0014] (4) In the improved ground described in any one of (1) to (3), The water-permeable pipe preferably includes a spirally wound frame member and a stretchable water-permeable membrane joined to the inner peripheral surface of the frame member.

[0015] In the present invention, the permeable pipe includes a spirally wound frame member and an expandable permeable membrane bonded to the inner peripheral surface of the frame member, so that even if the permeable pipe is pushed by water spurting out from the existing ground due to liquefaction during an earthquake, the permeable pipe can flex or expand flexibly, preventing damage. Therefore, water spurting out from the excavated existing ground due to liquefaction can be more reliably discharged into the drainage ditch.

[0016] (5) In the improved ground described in any one of (1) to (4), It is preferable that the longitudinal end of the permeable pipe is provided with a check valve that blocks water from flowing back from the drain groove.

[0017] In the present invention, the longitudinal end of the permeable pipe is equipped with a check valve that blocks water flowing back from the drainage ditch, thereby preventing rainwater and other water that has accumulated in the drainage ditch from flowing back into the permeable pipe, and ensuring that water that erupts from the local ground due to liquefaction during an earthquake is reliably discharged from the permeable pipe into the drainage ditch.

[0018] (6) In the improved ground described in any one of (1) to (5), It is preferable that the drainage groove has a depth and width of a water-permeable pipe communicating portion formed to be able to communicate with the water-permeable pipe greater than the depth and width of a general portion.

[0019] In the present invention, the drainage ditch is formed so that the depth and width of the permeable pipe connecting portion, which is formed to be able to communicate with the permeable pipe, are greater than the depth and width of the general portion, so even if a large amount of water gushing out from the existing ground during an earthquake is discharged from the permeable pipe into the permeable pipe connecting portion in a short period of time, the capacity of the permeable pipe connecting portion is greater than that of the general portion, so that drainage treatment is less likely to be hindered.As a result, water gushing out from the existing ground due to liquefaction during an earthquake can be discharged from the permeable pipe into the drainage ditch more quickly and reliably.

[0020] (7) In the construction method of improved ground described in any one of (1) to (6), This is a construction method for improved ground, comprising a ground excavation step of excavating the existing ground to a predetermined depth to form the groove portion; a permeable pipe installation step of installing a permeable pipe in the groove portion, the permeable pipe being formed so as to be able to communicate with a drainage ditch formed on the outer edge of the existing ground; a glass granulated sand burying step of burying the glass granulated sand in the groove portion and on the existing ground while surrounding the permeable pipe; a waterproof sheet member laying step of laying a waterproof sheet member that horizontally covers the upper surface of the glass granulated sand; and a cover soil laying step of laying cover soil on the waterproof sheet member.

[0021] In the present invention, the method includes a ground excavation step of excavating the existing ground to a predetermined depth to form a groove; a permeable pipe installation step of installing a permeable pipe in the groove, the permeable pipe being formed so as to be able to communicate with a drainage ditch formed on the outer edge of the existing ground; a glass granulated sand embedding step of burying glass granulated sand in the groove and on the existing ground while surrounding the permeable pipe; a waterproof sheet member laying step of laying a waterproof sheet member that horizontally covers the top surface of the glass granulated sand; and a cover soil laying step of laying cover soil on top of the waterproof sheet member.As a result, the waterproof sheet member can prevent water that springs up from the existing ground due to liquefaction during an earthquake from spraying upward, and water that accumulates on the underside of the waterproof sheet member can be guided into the permeable pipe via the glass granulated sand, allowing improved ground to be constructed efficiently in a short period of time. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide improved ground and a construction method thereof that can quickly drain water that springs up from excavated ground due to liquefaction into a drainage ditch, thereby reducing damage such as subsidence and floating of the ground. [Brief explanation of the drawings]

[0023] [Figure 1] This is an oblique view showing each layer of the improved ground according to this embodiment in a stepped cross section. [Figure 2] 2 is a cross-sectional view taken along the line AA in FIG. 1. [Figure 3] Figure 1 shows the particle size distribution diagram (JIS A 1204 particle size accumulation curve) of the glass granulated sand in the improved ground. [Figure 4] 3 is a cross-sectional view of FIG. 2 shown in FIG. [Figure 5] FIG. 2 is an enlarged cross-sectional view of a portion C shown in FIG. [Figure 6] FIG. 2 is a partial plan view of the permeable sheet member of the improved ground shown in FIG. [Figure 7] FIG. 2 is a partial perspective view of a net-like reinforcing member to be buried in the covering soil of the improved ground shown in FIG. 1. [Figure 8] FIG. 2 is a flowchart showing a construction method for improving the ground shown in FIG. 1. [Figure 9]FIG. 1 is a schematic cross-sectional view of the improved ground described in Patent Document 1. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. First, an example in which the improved ground according to the present embodiment is applied to a road will be described. Next, an example in which the construction method for improved ground according to the present embodiment is applied to a road will be described.

[0025] <Basic structure of this improved ground> First, the basic structure of the improved ground according to this embodiment (hereinafter referred to as "this improved ground") will be described with reference to Figures 1 to 7. Figure 1 shows a perspective view of each layer of the improved ground according to this embodiment, cross-sectioned in a stepped pattern. Figure 2 shows the AA cross section shown in Figure 1. Figure 3 shows a particle size distribution diagram (JIS A 1204 particle size accumulation curve) of the glass granulated sand in the improved ground shown in Figure 1. Figure 4 shows the BB cross section shown in Figure 2. Figure 5 shows an enlarged cross section of part C shown in Figure 1. Figure 6 shows a partial plan view of the permeable sheet member of the improved ground shown in Figure 1. Figure 7 shows a partial perspective view of a net-like reinforcing member to be buried in the cover soil of the improved ground shown in Figure 1.

[0026] As shown in Figures 1 and 2, this improved ground 10 includes glass granulated sand 2 buried on top of excavated existing ground 1 and in a groove 11 formed in the existing ground 1, a permeable pipe 3 surrounded by the glass granulated sand 2 and connected to a drainage ditch HK formed at the outer edge 12 of the existing ground 1, a waterproof sheet member 4 horizontally covering the glass granulated sand 2 above the permeable pipe 3, and cover soil 5 laid above the waterproof sheet member 4. Because this improved ground 10 is a road example, the glass granulated sand 2 buried on top of the existing ground 1 and in the groove 11 is compacted to the required hardness. An asphalt layer 7 is laid on top of the cover soil 5. The asphalt layer 7 is composed of a lower layer 71 and an upper layer 72.

[0027] In this improved ground 10, a waterproof sheet member 4 horizontally covers the glass granulated sand 2 surrounding the permeable pipe 3 and the glass granulated sand 2 on the existing ground 1, above the permeable pipe 3, which is formed to be able to communicate with the drainage ditch HK formed at the outer edge 12 of the existing ground 1. This prevents water SB from liquefying the existing ground 1 during an earthquake from escaping upward. Furthermore, water SB that accumulates on the underside of the waterproof sheet member 4 is guided through the glass granulated sand 2 into the permeable pipe 3, from which it is discharged into the drainage ditch HK. Furthermore, because the glass granulated sand 2 does not contain a large amount of silt or clay, as is the case with pit sand, it has excellent permeability and is less likely to clog the permeable pipe 3. Therefore, water SB that liquefies the excavated existing ground 1 can be quickly guided through the glass granulated sand 2 into the permeable pipe 3.

[0028] Furthermore, in this improved ground 10, the cover soil 5 is laid above the waterproof sheet member 4, so that it can resist the upward ejection force of water SB that springs up from the existing ground 1 due to liquefaction during an earthquake. As a result, it is possible to reduce the possibility of damage such as ground subsidence and floating due to liquefaction of the existing ground 1. Therefore, according to this improved ground 10, water SB that springs up from the excavated existing ground 1 due to liquefaction can be quickly discharged into the drainage ditch HK, reducing damage such as ground subsidence and floating.

[0029] Here, the in-situ ground 1 is intended to be soft ground such as sandy ground, but it is not necessarily limited to this, and can be ground such as reclaimed ground or raised ground that is prone to ground liquefaction caused by groundwater erupting during an earthquake. Furthermore, the in-situ ground 1 is not limited to a planned site for a road, as in this example, but can also be a site where a parking lot, a building, or other structure is to be constructed. Note that this improved ground 10 does not reinforce the entire soft ground, so if necessary, the in-situ ground 1 can be reinforced by driving piles or the like.

[0030] The grooves 11 formed in the existing ground 1 are formed at required intervals, to a depth that allows the permeable pipes 3 to be buried within the improved ground 10. In areas of the existing ground 1 that are prone to liquefaction, it is advisable to form the grooves 11 at narrow intervals. The grooves 11 are also formed continuously up to the drainage ditches HK formed in the outer edge 12 of the existing ground 1. The grooves 11 may be formed as straight grooves that are perpendicular to and arranged in parallel with the drainage ditches HK, or they may be formed as lattice-like grooves that intersect vertically and horizontally. In this example, they are formed as lattice-like grooves.

[0031] The drainage ditch HK also has a bottom wall 13, an inner wall 14 that defines the boundary of the improved ground 10, and an outer wall 15 that abuts against the outer edge 12 of the existing ground 1, forming a U-shaped cross section. A permeable pipe 3 penetrates the inner wall 14, allowing communication between the permeable pipe 3 and the drainage ditch HK. The drainage ditch HK preferably has a permeable pipe connecting portion HK1 that is connected to the permeable pipe 3 and has a greater depth and width than the general portion HK2. This is because even if a large amount of water SB that erupts from the existing ground 1 during an earthquake is discharged from the permeable pipe 3 in a short period of time, it will not hinder drainage treatment.

[0032] The glass granulated sand 2 refers to glass sand formed into granules by crushing waste glass such as glass bottles and glass plates. When crushing the waste glass, sharp corners of the glass granulated sand 2 are rounded. As shown in FIG. 3, the glass granulated sand 2 is preferably formed to have a particle size d of approximately 0.1 mm (millimeter) to 5.0 mm. Here, the particle size d refers to the maximum dimension of the external shape of a single piece of the glass granulated sand 2. Since the particle size d is formed to approximately 0.1 mm to 5.0 mm, good permeability and compactibility can be achieved.

[0033] Furthermore, it is even more preferable that the particle size distribution of the glass granulated sand 2 be such that 30±5% of the particles have a particle size d of less than 1.0 mm, with the remainder having a particle size d of 1.0 mm or more and 5.0 mm or less. Since 65 to 75% of the particles have a particle size d of 1.0 mm or more and 5.0 mm or less, permeability is improved. Furthermore, since 30±5% of the particles have a particle size d of less than 1.0 mm, particles with a particle size d of less than 1.0 mm can fill the gaps between particles with a particle size d of 1.0 mm or more and 5.0 mm or less, improving compaction properties.

[0034] The waterproof sheet member 4 is formed, for example, from a thermoplastic resin (such as high-density polyethylene), and includes a base portion 42 formed in the shape of a flat sheet, and a plurality of raised portions 41 rising upward from the base portion 42. In this example, the raised portions 41 are formed in a truncated cone shape, but this is not limited to this and may be formed, for example, in an arc shape, a square tube shape, a cylindrical shape, or the like. The waterproof sheet member 4 can be extended to the required length by preparing a plurality of waterproof sheet members 4 formed to a predetermined length and overlapping the raised portions 41T formed in a cylindrical shape at the longitudinal ends with each other at the connecting portions 4S.

[0035] As shown in FIG. 1, the cover soil 5 is composed of a lower cover soil 51 and an upper cover soil 52 laid on top of a waterproof sheet member 4, with a net-like reinforcing member 53 sandwiched between them. The lower cover soil 51 and the upper cover soil 52 are preferably made of the glass granulated sand 2 described above. Natural sand, such as mountain sand, can be used for the cover soil 5, but mountain sand is laborious to collect and prone to environmental problems. In contrast, glass granulated sand 2 made from waste glass has the advantage of generating less carbon dioxide and being less likely to cause the environmental problems described above. The particle size distribution of the glass granulated sand 2 used for the cover soil 5 may be similar to that of the glass granulated sand 2 buried on the existing base 1 and in the groove 11 described above, but the particle size d may be approximately 0.1 mm to 10.0 mm.

[0036] 7, the net-like reinforcing member 53 is made up of multiple vertical strings 531 (for example, two strings) extending in the longitudinal direction of the improved ground 10 and a single horizontal string 532 extending in the width direction (short direction) of the improved ground 10, which cross each other in a grid pattern, and the intersections 533 are fastened together with thread or the like. In this example, the ground is being improved for a road, so the vertical strings 531 are two strings and the horizontal string 532 is one string, thereby increasing the strength of the road in the longitudinal direction.

[0037] As shown in Figures 1, 2, and 4, the improved ground 10 preferably includes a water-permeable sheet member 6, bonded to the underside of the waterproof sheet member 4 and arranged horizontally, between the waterproof sheet member 4 and the glass granulated sand 2. Here, the water-permeable sheet member 6 is bonded to the base portion 42 of the waterproof sheet member 4, creating a space capable of retaining water between the waterproof sheet member 6 and the raised portion 41 of the waterproof sheet member 4. In this case, moisture SB that accumulates on the underside of the waterproof sheet member 4 can be guided into the water-permeable pipe 3 via the water-permeable sheet member 6 and the glass granulated sand 2, and then discharged from the water-permeable pipe 3 into the drainage ditch HK. Therefore, moisture SB that seeps out from the excavated ground 1 due to liquefaction can be more quickly discharged into the drainage ditch HK.

[0038] The water-permeable sheet member 6 is preferably made of resin fibers such as polypropylene, and is preferably a sheet member woven in a plain weave pattern in which vertical bands 61 woven into flat bands of a predetermined width and horizontal bands 62 woven into flat bands of a predetermined width alternately cross each other, as shown in Figure 6. By weaving the vertical bands 61 and horizontal bands 62 into a plain weave pattern in which the vertical bands 61 and horizontal bands 62 alternately cross each other, the strength of the water-permeable sheet member 6 can be increased while ensuring water permeability. Furthermore, the strength of the waterproof sheet member 4 to which the water-permeable sheet member 6 is joined is improved, and durability against the water pressure of water SB that gushes out from the on-site ground 1 during an earthquake can be improved.

[0039] In the improved ground 10, the permeable pipe 3 preferably includes a spirally wound frame member 31 and an expandable permeable membrane 32 bonded to the inner circumferential surface of the frame member 31. In this case, even if the permeable pipe 3 is pushed by water SB, etc., that erupts from the existing ground 1 due to liquefaction during an earthquake, the permeable pipe 3 can flex or expand flexibly, avoiding breakage. Therefore, the water SB that springs from the excavated existing ground 1 due to liquefaction can be more reliably discharged into the drainage ditch HK. The frame member 31 is preferably formed of a resin material such as polypropylene and has a W-shaped cross section with two radially protruding projections, as shown in Figure 4. This is because the glass granulated sand 2 is inserted into the W-shaped valley, improving the prevention of misalignment of the permeable pipe 3 relative to the recessed groove 11 in which the glass granulated sand 2 is embedded. The expandable permeable membrane 32 has a hydraulic conductivity of, for example, 1.4 × 10 -2 It is recommended to use a polypropylene filter with a flow rate of about cm / sec.

[0040] Furthermore, in this improved ground 10, it is preferable that the longitudinal end 3T of the permeable pipe 3 is provided with a check valve 3G that blocks water from flowing back from the drainage ditch HK. In this case, rainwater and other water that has accumulated in the drainage ditch HK can be prevented from flowing back into the permeable pipe 3, and water SB that erupts from the existing ground 1 due to liquefaction during an earthquake can be reliably discharged from the permeable pipe 3 into the drainage ditch HK. The check valve 3G is formed from a circular resin plate such as polypropylene, and as shown in Figure 5, has a fixed part 3G1 fixed to the longitudinal end 3T of the permeable pipe 3 and an opening / closing part 3G2 connected via a notched hinge part 3G3.

[0041] <Construction method for this improved ground> Next, the construction method for improving ground according to this embodiment will be described with reference to Figures 1 to 8. Figure 8 shows a flow chart illustrating the construction method for improving ground shown in Figure 1.

[0042] The construction method for the improved ground 10 includes a ground excavation step S1 in which the existing ground 1 is excavated to a predetermined depth to form a groove portion 11; a permeable pipe installation step S2 in which a permeable pipe 3 formed so as to be able to communicate with a drainage ditch HK formed on the outer edge portion 12 of the existing ground 1 is installed in the groove portion 11; a glass granulated sand burying step S3 in which glass granulated sand 2 is buried in the groove portion 11 and on the existing ground 1 while surrounding the permeable pipe 3; a waterproof sheet member laying step S4 in which a waterproof sheet member 4 is laid to horizontally cover the upper surface of the glass granulated sand 2; and a cover soil laying step S5 in which cover soil 5 is laid on the waterproof sheet member 4.

[0043] Specifically, in the ground excavation step S1, the in-place ground 1 is excavated to a predetermined depth to form a trench 11, so that water SB that springs up from the in-place ground 1 due to liquefaction during an earthquake can be collected in the trench 11. In addition, in the permeable pipe installation step S2, a permeable pipe 3 formed to be able to communicate with a drainage ditch HK formed in the outer edge 12 of the in-place ground 1 is installed in the trench 11, so that water SB collected in the trench 11 can be discharged via the permeable pipe 3 to the drainage ditch HK formed in the outer edge 12 of the in-place ground 1. In addition, in the glass granulated sand burying step S3, glass granulated sand 2 is buried in the trench 11 and on the in-place ground 1 while surrounding the permeable pipe 3. Therefore, while the permeable pipe 3 is protected by the glass granulated sand 2, water SB collected in the trench 11 can be guided into the permeable pipe 3 through gaps in the glass granulated sand 2 by capillary action.

[0044] Furthermore, the waterproof sheet member laying process S4 involves laying a waterproof sheet member 4 horizontally covering the top surface of the glass granulated sand 2. This prevents water SB from liquefying the existing ground 1 during an earthquake from gushing upward, and also guides water SB that accumulates on the underside of the waterproof sheet member 4 into the permeable pipe 3 via the glass granulated sand 2. Furthermore, the soil cover laying process S5 involves laying soil cover 5 on top of the waterproof sheet member 4, which can resist the upward gushing force of water SB from liquefying the existing ground 1 during an earthquake. As a result, the possibility of damage such as ground subsidence and floating due to liquefaction of the existing ground 1 is reduced. Therefore, this construction method for improved ground 10 allows water SB from the excavated existing ground 1 to be quickly drained into the drainage ditch HK, thereby enabling efficient construction of improved ground 10 in a short period of time, reducing damage such as ground subsidence and floating.

[0045] <Action and effect> As described above in detail, in the improved ground 10 according to this embodiment, the waterproof sheet member 4 horizontally covers the glass granulated sand 2 surrounding the permeable pipe 3 and the glass granulated sand 2 on the existing ground 1 above the permeable pipe 3, which is formed to be able to communicate with the drainage ditch HK formed at the outer edge 12 of the existing ground 1. This prevents water SB from liquefying the existing ground 1 during an earthquake from escaping upward. Furthermore, water SB that accumulates on the underside of the waterproof sheet member 4 can be guided into the permeable pipe 3 via the glass granulated sand 2, allowing it to be quickly drained from the permeable pipe 3 to the drainage ditch HK. Furthermore, because the glass granulated sand 2 does not contain a large amount of silt or clay, as is the case with pit sand, it has excellent permeability and is less likely to clog the permeable pipe 3. Therefore, water SB that liquefies the excavated existing ground 1 can be quickly guided into the permeable pipe 3 via the glass granulated sand 2. As a result, the possibility of damage such as subsidence or floating of the ground due to liquefaction of the existing ground 1 can be reduced.

[0046] Therefore, according to this embodiment, water SB that springs up from the excavated existing ground 1 due to liquefaction can be quickly discharged into the drainage ditch HK, and an improved ground 10 can be provided that can reduce damage such as subsidence and floating of the ground.

[0047] Furthermore, according to this embodiment, a water-permeable sheet member 6 is provided between the waterproof sheet member 4 and the glass granulated sand 2, and is joined to the underside of the waterproof sheet member 4 and arranged horizontally. This allows the moisture SB that accumulates on the underside of the waterproof sheet member 4 to be guided into the water-permeable pipe 3 via the water-permeable sheet member 6 and the glass granulated sand 2, and then discharged from the water-permeable pipe 3 into the drainage ditch HK. Therefore, the moisture SB that springs from the excavated on-site ground 1 due to liquefaction can be discharged even more quickly into the drainage ditch HK.

[0048] Furthermore, according to this embodiment, the particle size distribution of the glass granulated sand 2 is such that 30±5% of the total particles have a particle size d of less than 1.0 mm, with the remainder having a particle size d of 1.0 mm or more and 5.0 mm or less. This allows for both permeability and compactibility. That is, since 65 to 75% of the particles have a particle size d of 1.0 mm or more and 5.0 mm or less, permeability is improved. Furthermore, since 30±5% of the particles have a particle size d of less than 1.0 mm, particles with a particle size d of less than 1.0 mm can fill the gaps between particles with a particle size d of 1.0 mm or more and 5.0 mm or less, improving compactibility.

[0049] Furthermore, according to this embodiment, the permeable pipe 3 includes a spirally wound frame member 31 and an expandable permeable membrane 32 connected to the inner peripheral surface of the frame member 31. Therefore, even if the permeable pipe 3 is pushed by water SB that erupts from the existing ground 1 due to liquefaction during an earthquake, the permeable pipe 3 can flex or expand flexibly, thereby avoiding damage. Therefore, the water SB that springs from the excavated existing ground 1 due to liquefaction can be more reliably discharged to the drainage ditch HK.

[0050] Furthermore, according to this embodiment, the longitudinal end 3T of the permeable pipe 3 is provided with a check valve 3G that blocks water flowing back from the drainage ditch HK, thereby preventing rainwater and the like that has accumulated in the drainage ditch HK from flowing back into the permeable pipe 3, and moisture SB that erupts from the existing ground 1 due to liquefaction during an earthquake can be reliably discharged from the permeable pipe 3 into the drainage ditch HK.

[0051] Furthermore, according to this embodiment, the drainage ditch HK has a larger groove depth and width for the permeable pipe communicating portion HK1, which is formed to be able to communicate with the permeable pipe 3, than for the general portion HK2. Therefore, even if a large amount of water SB spurting from the on-site ground 1 during an earthquake is discharged in a short period of time from the permeable pipe 3 to the permeable pipe communicating portion HK1, the capacity of the permeable pipe communicating portion HK1 is larger than that of the general portion HK2, which makes it less likely to cause a disruption to drainage treatment. Therefore, water SB spurting from the on-site ground 1 due to liquefaction during an earthquake can be discharged from the permeable pipe 3 to the drainage ditch HK more quickly and reliably.

[0052] According to the construction method for improved ground of this other embodiment, there are a ground excavation step S1 in which the existing ground 1 is excavated to a predetermined depth to form a recessed trench 11, a permeable pipe installation step S2 in which a permeable pipe 3 formed so as to be able to communicate with a drainage ditch HK formed in an outer edge portion 12 of the existing ground 1 is installed in the recessed trench 11, a glass granulated sand burying step S3 in which glass granulated sand 2 is buried in the recessed trench 11 and on the existing ground 1 while surrounding the permeable pipe 3, and a waterproof sheet member 4 for horizontally covering the upper surface of the glass granulated sand 2. The method includes a waterproof sheet member laying step S4 for laying a waterproof sheet member 4 on the existing ground 1, and a cover soil laying step S5 for laying cover soil 5 on the waterproof sheet member 4. Therefore, the waterproof sheet member 4 can prevent the water SB that springs up from the existing ground 1 due to liquefaction during an earthquake from spraying upward, and the water SB that accumulates on the underside of the waterproof sheet member 4 can be guided into the permeable pipe 3 via the glass granulated sand 2, and can be discharged from the permeable pipe 3 to the drainage ditch HK, thereby efficiently constructing an improved ground 10 in a short period of time. [Industrial Applicability]

[0053] The present invention can be used, for example, as an improved ground for improving the foundation of a road or the like built on soft ground that is predicted to liquefy in an earthquake or the like, and as a construction method for the same. [Explanation of symbols]

[0054] 1 Local Edition 2. Glass granulated sand 3 Water permeable pipe 3G check valve 3T Longitudinal end 4 Waterproof sheet materials 5 Soil cover 6 Permeable sheet material 10 Improved ground 11 Groove 12 outer edge 31 Frame members 32 Stretchable water permeable membrane HK drain HK1 Water permeable pipe communication section HK2 General Department S1 Ground excavation process S2 Water permeable pipe installation process S3 Glass granulated sand burying process S4 Waterproof sheet component laying process S5 Soil covering process

Claims

1. An improved ground comprising: glass granulated sand buried on top of an excavated existing ground and in a groove formed in the existing ground; a permeable pipe surrounded by the glass granulated sand and formed so as to be able to communicate with a drainage ditch formed on the outer edge of the existing ground; a waterproof sheet member horizontally covering the top surface of the glass granulated sand above the permeable pipe; and covering soil laid above the waterproof sheet member.

2. In the improved ground according to claim 1, Improved ground characterized by a water-permeable sheet member that is joined to the underside of the waterproof sheet member and arranged horizontally between the waterproof sheet member and the glass granulated sand.

3. In the improved ground according to claim 1, The particle size distribution of the glass granulated sand is such that 30±5% of the total is less than 1.0 mm, and the remainder is 1.0 mm or more and 5.0 mm or less.

4. In the improved ground according to claim 1, The improved ground is characterized in that the permeable pipe comprises a spirally wound frame member and an elastic permeable membrane joined to the inner surface of the frame member.

5. In the improved ground according to claim 1, Improved ground characterized in that the end of the permeable pipe is provided with a check valve to block water from flowing back from the drainage ditch.

6. In the improved ground according to claim 1, The drainage ditch is characterized in that the depth and width of the permeable pipe connection portion, which is formed to be able to communicate with the permeable pipe, are greater than the depth and width of the general portion.

7. The method for constructing improved ground according to any one of claims 1 to 6, a ground excavation step of excavating the existing ground to a predetermined depth to form the groove; a permeable pipe installation step of installing a permeable pipe in the groove, the permeable pipe being formed so as to be able to communicate with a drainage ditch formed on the outer edge of the existing ground; a glass granulated sand burying step of burying the glass granulated sand in the groove and on the existing ground while surrounding the permeable pipe; a waterproof sheet member laying step of laying a waterproof sheet member that horizontally covers the upper surface of the glass granulated sand; and a soil covering step of laying soil on the waterproof sheet member.

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