JP2014163062A - Method for preventing liquefaction of subgrade - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preventing liquefaction of a subgrade, allowing liquefaction prevention of the subgrade of an existing facility such as a road or airport facility at low cost, and capable of minimizing a nonoperating period of the existing facility and suppressing an influence on the existing facility to the minimum.SOLUTION: In a method for preventing liquefaction of a subgrade, the following steps are repeated: a drilling step for forming a drain material burying hole 6 passing through an existing pavement part B and arriving at a desired depth of the subgrade A; a drain material burying step for inserting a drain material 1 into the drain material burying hole 6 to bury the drain material 1 in the subgrade A; and a temporary pavement step for blocking an upper end opening part of the drain material burying hole 6 by a temporary pavement material 21. Then, the predetermined number of drain materials 1, 1... are buried successively in the subgrade A below an existing pavement part B. Thereafter, the existing pavement part B and the temporary pavement materials 21 are removed and a new pavement part 3 is constructed on the subgrade A.

Description

  The present invention relates to a ground liquefaction prevention method for applying liquefaction prevention measures to the ground of an existing facility where a ground surface portion such as a road or an airport facility is paved.

  Conventionally, in the ground such as sandy ground, the pressure between water and sand particles in the ground (pore water) suddenly increases due to the impact of earthquake motion, etc., causing the balance between the sand and sand particles to be lost, and the sand and sand behave like a liquid. That is, the phenomenon of ground liquefaction is regarded as a problem.

  From the viewpoint of disaster prevention, it is necessary to take measures to prevent liquefaction of the ground in advance, especially in coastal areas where there is concern about liquefaction such as landfills. Because it exists over a wide area, measures to prevent liquefaction are urgently needed.

  On the other hand, there are many grounds under existing facilities such as roads and airport facilities as countermeasures for liquefaction prevention, and measures to prevent liquefaction to the ground are implemented while minimizing the impact on the operation of such existing facilities. There is a need.

  As a liquefaction prevention method for the ground under such existing facilities, a chemical solution injection method for injecting a special chemical solution into the ground to consolidate the ground is known (see, for example, Patent Document 1).

  In this chemical injection method, a small-diameter chemical injection hole for chemical injection is drilled through the existing pavement, and the chemical injection into the ground is performed through the injection pipe into the chemical injection hole. By performing the work at night, the impact on the operation of the existing facilities can be suppressed.

  In addition, as another liquefaction prevention method, a plurality of drainage materials having water permeability in the ground are embedded at intervals in the vertical direction, and excess pore water generated by impact such as seismic motion on the drain material. There is known a drainage drain construction method in which an increase in pore water pressure is suppressed by injecting water (for example, see Patent Document 2).

  In this drainage drain method, after removing the pavement in a certain area where liquefaction is a concern by excavation etc. to expose the ground surface, multiple drain materials are buried in the ground at intervals from each other. After the drain material is buried, a drainage layer having water permeability is formed by pulverizing stones or the like on the ground surface, and further re-paved with asphalt or the like on the drainage layer.

Japanese Patent Laid-Open No. 10-88561 JP-A-63-19320

  However, the conventional liquefaction prevention method (chemical solution injection method) using a chemical solution as described above uses a special chemical solution, so the construction cost is very expensive compared to other methods, and measures to prevent liquefaction. It was an impediment to promotion.

  On the other hand, in the case of the conventional drainage drain method, in order to embed a large number of drain materials in a certain range of ground, the ground surface of the construction target area is exposed by first removing the paving part such as asphalt covering the ground surface. After removing the pavement, the function of facilities such as roads is lost, so there was a problem that the operation of existing facilities had to be suspended for a long time during a series of construction periods. .

  In view of such conventional problems, the present invention can be constructed at low cost to prevent liquefaction of the ground in existing facilities such as roads and airport facilities, and the operation suspension period of the existing facilities is kept to a minimum, It was made for the purpose of providing a ground liquefaction prevention method that can minimize the impact on facility operation.

  The feature of the invention according to claim 1 for solving the conventional problem as described above is that a plurality of drain materials having water permeability are embedded vertically in the ground below the pavement, and the pore water pressure in the ground is reduced. In the ground liquefaction prevention method that can suppress the rise, a drilling step of forming a drain material buried hole that penetrates an existing pavement and reaches a desired depth of the ground, and the drain material buried The drain material burying step of inserting the drain material into the hole and burying the drain material in the ground, and the temporary paving step of closing the upper end opening of the drain material burying hole with the temporary paving material are repeated, A predetermined number of the drain materials are sequentially embedded in the ground below the pavement, and then the existing pavement and temporary pavement are removed to construct a new pavement on the ground.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect, after the existing pavement is removed, the surface portion of the ground is dug down to a desired depth, and then on a new ground surface. Forming a horizontal drainage portion having water permeability through which the upper end of each drain material communicates, and constructing a new pavement portion on the horizontal drainage portion.

  According to a third aspect of the present invention, in addition to the structure of the first or second aspect, in the drilling step, the drain material embedding hole is formed by embedding a tubular drill rod in the ground, and the drain In the material embedding process, after the drain material is inserted into the drilling rod, the draining material is embedded in the ground by pulling out the drilling rod from the drain material embedding hole.

  According to a fourth aspect of the present invention, in addition to the configuration of the first, second, or third aspect, in the temporary paving step, an upper end inner peripheral portion of the drain material embedding hole surrounds the periphery of the drain material upper end portion. A cylindrical protective member is installed in the drainage material embedding hole and the upper end opening of the protective member with the temporary paving material.

  In the ground liquefaction prevention method according to the present invention, as described above, a plurality of drain materials having water permeability are embedded vertically in the ground below the pavement so as to suppress an increase in pore water pressure in the ground. In the ground liquefaction prevention construction method, a drilling step of forming a drain material buried hole that penetrates an existing pavement and reaches a desired depth of the ground, and the drain material in the drain material buried hole A drain material burying step of burying the drain material in the ground and inserting a temporary pavement step of closing the upper end opening of the drain material burying hole with a temporary pavement material, in the ground under the existing pavement portion After burying a predetermined number of the drain materials in order, the existing pavement and temporary pavement are removed, and a new pavement is constructed on the ground, so that it is located under existing facilities such as roads and airport facilities. Inexpensive to the ground It can be subjected to a liquefaction prevention measures. In addition, the upper end of the buried drain material is prevented from being exposed to the pavement surface, and even if a vehicle or the like passes over the existing pavement, the drain material is protected without impairing its function. The material can be buried while maintaining the function of the existing pavement, and the removal and re-paving processes of the existing pavement are concentrated in a short period of time. The operation suspension period can be greatly shortened, and the effect on the facility operation due to the suspension can be suppressed.

  Further, in the present invention, after removing the existing pavement portion, the surface portion of the ground is dug down to a desired depth, and then, the water permeability in which the upper end of each drain material is communicated with the new ground surface. By forming a horizontal drainage section with a new pavement section on the horizontal drainage section, the upper end of each drain material communicates between the pavement section and the ground surface, and drainage is possible in the horizontal direction. A simple horizontal drainage part can be constructed in a short period of time, and excess pore water in the ground can be dissipated through the drain material and the horizontal drainage part, so that the increase in pore water pressure in the ground can be suppressed and the effect of preventing liquefaction can be enhanced. .

  Furthermore, in the present invention, in the drilling step, the drain material embedding hole is formed by embedding a tubular drill rod in the ground, and in the drain material embedding step, the drain material is inserted into the drill rod. Then, the drain material can be embedded in the ground efficiently from the existing pavement by embedding the drain material in the ground by pulling out the drilling rod from the drain material embedding hole. .

  Furthermore, in the present invention, in the temporary paving step, a cylindrical protective member is installed so as to surround the periphery of the upper end portion of the drain material on the inner periphery of the upper end of the drain material embedding hole, and the drain material is in that state. By closing the upper end opening of the buried hole and the protection member with temporary pavement material, the upper end portion of the drain material is protected from the load of the vehicle etc. passing through the pavement and the ground pressure, and the drainage function of the drain material is impaired. Can be prevented.

(A)-(d) is a schematic sectional drawing which shows the state of each process of the liquefaction prevention construction method of the ground which concerns on this invention, Comprising: (a) is a drilling process, (b), (c) is drain material. (D) is a figure which shows a temporary paving process. It is an expanded sectional view which shows the state of the temporary pavement part in FIG.1 (d). (E)-(h) is a schematic sectional drawing which shows the state of each process of this invention method, (e) is the state at the time of operation of existing facilities, (f) is an existing pavement excavation process, (g) Is a figure which shows the state of a drainage part creation process, (h) is a repaving process.

  Next, an embodiment of the ground liquefaction prevention method according to the present invention will be described based on the examples shown in FIGS. In addition, the code | symbol A in the figure is the ground which liquefaction of sandy ground etc. concerns, and the code | symbol B is the existing pavement part formed on the ground A. In FIG.

  The ground liquefaction prevention method according to the present invention is a method of applying liquefaction prevention measures to the ground A of existing facilities such as roads and airport facilities where the surface portion is paved. A plurality of columnar drain materials 1, 1... Are embedded in a vertical direction and spaced apart from each other, so that excess pore water generated in the ground A due to an impact such as earthquake motion can be removed. 1 to dissipate quickly, suppress excessive increase of pore water pressure, and prevent ground A from liquefaction.

  In the method of the present invention, as a preliminary preparation, first, the ground layer where liquefaction is a concern is investigated, the depth of the ground where liquefaction measures need to be taken is specified, and the length according to the depth is determined. That is, when the lower end reaches the lower end of the construction target stratum, drain materials 1, 1... Having a length at which the upper end is located at the upper end portion of the construction target stratum are prepared.

  The drain materials 1, 1... Are formed in a column shape or a hollow column shape having water permeability, and for example, a cylindrical column shape shown in FIG.

  The drain members 1, 1... Are formed in a hollow cylindrical column shape by a filter material 2 made of a synthetic resin having water permeability, and are reinforced by a reinforcing body 3 whose inner peripheral surface portion or outer peripheral surface portion is formed in a spiral shape. ing.

  Further, the opening portions at both ends of the drain materials 1, 1... Are closed by the lid member 4 so that earth and sand cannot enter the drain materials 1, 1.

  The drain members 1, 1... Are not limited to the embodiment shown in FIG. 3, and may be, for example, those having a rectangular cross section.

  Next, the drain material 1, 1... Is buried a plurality of times, and a predetermined number of the drain materials are provided in the ground A under the existing pavement B in a certain area where the liquefaction prevention measures are taken. Embed 1,1, ... Each operation is performed every limited time period such as at night when the traffic is low.

  As shown in FIG. 1 (a), the embedding operation of each drain material 1, 1... First penetrates the existing pavement B using the drilling device 5 and the desired depth of the ground A. The drain material embedding hole 6 reaching the depth is formed (drilling step).

  The hole drilling device 5 includes, for example, a vehicle unit 10 that can be moved by a crawler, a guide shell 12 that is supported in front of the vehicle unit 10 via a boom 11, and a hole that is movably supported by the guide shell 12. A unit 13 and a tubular drilling rod 14 whose upper end is detachably held by the drilling unit 13 are provided, and the drilling rod 13 is rotated by the drilling unit 13 and strikes in the drilling axis direction. The drilling rod 14 is embedded in the ground A while drilling the existing pavement B and the ground A.

  The drilling rod 14 is formed in a tubular shape with both ends having an inner diameter slightly larger than the outer diameter of the drain material 1, 1... By the steel pipe, and the pavement part B is hit against the pavement part B by the drilling unit 13. The asphalt concrete etc. that constitute the slab are crushed and the debris is taken into the inside from the lower end opening, and the ground A is taken into the inside from the lower end opening by embedding the drilling rod 14 in the ground. .

  Further, the hole drilling device 5 is provided with a soil discharging means for discharging the remnants of the pavement part B and the earth and sand taken into the hole drilling rod 14 to the outside from the upper end opening of the hole drilling rod 14, and the earth and sand etc. discharged The drain members 1, 1... Can be inserted into the hole rod 14.

  The earth discharging means uses, for example, a jet nozzle inserted into the inside of the drilling rod 14 from the upper end opening, and jets jet water from the jet nozzle toward the earth and sand taken into the drilling rod 14. Thus, the debris or earth and sand are discharged from the upper end opening to the outside of the drilling rod 14 by riding on the water flow by the jet water.

  In the drilling operation using such a drilling device 5, first, the position of the lower end of the drilling rod 14 is aligned with a predetermined position of the existing pavement B that covers the surface of the ground A, and the drilling rod 14 is moved at that position. The pavement penetrating portion 15 that penetrates the existing pavement portion B is formed by rotating and giving a blow in the direction of the drilling axis.

  Subsequently, while rotating and hitting the drilling rod 14 that has reached the surface of the ground A through the pavement penetrating portion 15, a position that reaches a desired depth in the ground A, that is, a depth at which the liquefaction may occur. The buried hole main body portion 16 that is continuous with the pavement penetrating portion 15 is formed.

  At that time, the drilling rod 14 is embedded while discharging the earth and sand in the drilling rod 14 by the soil discharging means, and the embedded hole main body 16 is in a state where the inner peripheral portion is covered with the drilling rod 14. It is formed.

  As a result, a drain material embedding hole 6 that penetrates the existing pavement B and reaches a desired depth in the ground A is formed, and a drilling rod 14 is formed on the inner peripheral portion of the drain material embedding hole 6. Installed.

  The length of the drill rod 14 is formed longer than the total length of the drain material 1, 1... And the entire depth of the drain material buried hole 6, and when the lower end of the drill rod 14 reaches a desired depth. Moreover, the upper end portion of the drilling rod 14 has a length protruding from the surface of the existing pavement portion B.

  When the formation of the drain material embedding hole 6 and the embedding of the drilling rod 14 into the ground A are completed, as shown in FIGS. 1B to 1C, the drain materials 1, 1. The drain material 1, 1 ... is embedded in the ground A by inserting into the hole 6 (drain material embedding step).

  In this drain material embedding step, as shown in FIG. 1 (b), the drilling unit 13 is removed from the upper end portion of the drilling rod 14, and the drain materials 1, 1,. And is pushed in until the lower end of the drain material 1, 1... Reaches a desired depth, that is, the lower end of the drain material embedding hole 6.

  In that case, the earth and sand in the drilling rod 14 is removed by the earth removing means, and the drilling rod 14 prevents the earth and sand from collapsing in the inner periphery of the drain material embedding hole 6. The drain material 1, 1... Can be preferably inserted into the drain material embedding hole 6 without receiving pressure.

  Then, as shown in FIG. 1C, the drilling rod 14 is pulled out from the ground A, and the drain materials 1, 1... Are embedded in the ground A.

  At this time, since the earth and sand taken into the drilling rod 14 is removed by the earth discharging means and the lower end is opened, the ground A (with the drain material 1 left in the drain material embedding hole 6) It can be pulled out from the drain material buried hole 6).

  Further, when pulling out the drilling rod 14, the above-described drilling device 5 is used to rotate the drilling rod 14 and pull it out while vibrating in the direction of the drilling shaft, thereby smoothly removing the drilling rod 14. Can be pulled out.

  Next, as shown in FIGS. 1D and 2, the upper end opening of the drain material embedding hole 6 is closed with the temporary pavement material 21, and the existing pavement B is temporarily restored to a usable state (temporary pavement step). ).

  In this temporary paving process, first, a cylindrical protective member 20 such as a pipe made of vinyl chloride is installed on the inner peripheral portion of the drain material embedding hole 6 and outside the upper end portion of the drain material 1, 1. The upper ends of the drain materials 1, 1... Are protected from the pressure of the ground A.

  This protective member 20 is installed across the pavement penetration part 15 of the drain material embedding hole 6 and the embedding hole main body part 16 so that the lower end reaches the planned excavation depth C indicated by a one-dot chain line in the figure. Install.

  Then, by fixing the flat lid-like temporary pavement material 21 to the upper end surface of the protective member 20, the upper end opening of the protective member 20 is closed, and further, the outer peripheral surface portion of the temporary pavement material 21 and the drain material buried hole 6 are closed. Between them, a filling material 22 such as mortar is filled, and the surface opening of the drain material embedding hole 6 is closed by the temporary paving material 21. In that case, the temporary pavement material 21 is installed so that it may become a surface position substantially the same as the surface of the existing pavement part B.

  The temporary pavement 21 is made of a steel plate or the like, has a strength capable of withstanding the load of a vehicle or the like passing over the existing pavement B, and can maintain the existing pavement B in a usable state. Yes.

  Further, by covering the upper end opening of the drain material embedding hole 6 with the temporary pavement material 21, it is possible to prevent the upper end portions of the buried drain materials 1, 1. Even if a vehicle or the like passes over B, the drain materials 1, 1... Are protected without impairing their functions.

  Then, the drilling device 5 is moved and the series of steps shown in FIGS. 1A to 1D are repeated, and the number of drain materials 1, 1... I will do it.

  After the completion of the burial operation of each drain material 1, 1..., The portion where each drain material 1, 1. The function of the existing pavement part B is impaired in the part where the upper end opening is blocked by the temporary pavement material 21 and the function of the existing pavement part B is maintained, and the drain material 1, 1. Therefore, the area can be released and the existing facilities can be operated during the daytime when there is a lot of traffic.

  Then, after the above-described series of drain material burying operations are repeated, and all the drain materials 1, 1... Have been buried in the ground A of the fixed area where liquefaction prevention measures are applied, the fixed region where liquefaction prevention measures are applied. As shown in FIGS. 3E to 3F, the existing pavement B is scraped off by excavation to expose the surface of the ground A.

  Further, the surface portion of the ground A is dug down to the planned excavation depth C, the surface D of the new ground A is exposed, and the newly exposed ground surface D is compacted.

  At that time, the temporary paving material 21 and the protection member 20 are left and excavation is performed in a state where the upper ends of the drain materials 1, 1... Are protected, and the drainage function of the drain materials 1, 1. Like that.

  Then, after the newly exposed ground surface portion D is compacted, the temporary paving material 21 and the protection member 20 are removed, and the upper end portions of the drain materials 1, 1... Are projected from the new ground surface D. .

  Next, as shown in FIG. 3G, a horizontal drainage portion 30 having water permeability is formed on the surface D of the new ground A so that the upper ends of the drain materials 1, 1.

  The horizontal drainage part 30 is formed in a layered manner by laying a large number of crushed stones 31, 31... On the ground A, for example, so that water flows through the gaps between the crushed stones 31, 31. Moreover, the upper end part of each drain material 1,1 ... is embed | buried between the crushed stones 31,31 ..., and the upper end part of the drain material 1,1 ... is connected.

  Finally, as shown in FIG. 3 (h), a pavement material such as asphalt concrete is laid on the horizontal drainage portion 30 to construct a new pavement portion E, and the liquefaction prevention structure of the ground A is completed.

  In the ground liquefaction prevention method constructed as described above, each drain material 1, 1... Can be buried while the function of the existing pavement B is ensured, and the existing pavement B is removed. Since the installation and re-paving of the horizontal drainage unit 30 are concentrated in a certain period, the operation suspension period of existing facilities such as roads and airport facilities is greatly shortened, and the effect on the facility operation due to the suspension is reduced. Can do.

  In addition, although the above-mentioned Example demonstrated the example which forms the horizontal drainage part 30 by digging the ground A surface part and laying the crushed stone 31,31 ... there, a horizontal drainage part is an Example mentioned above. For example, a plurality of tubular horizontal drainage members may be embedded in the surface portion of the ground A in the horizontal direction, and the upper end portion of each drain member 1 may be connected to each horizontal drainage member. .

  Further, in the above-described embodiment, an example in which a flat temporary paving material is used has been described. However, a lower surface integrally provided with a cylindrical drain protection portion in which the temporary paving material is raised from the peripheral edge of the flat main body portion. It may be formed in an inverted bottomed cylindrical shape having an opening and having a function of a protective member.

  Further, in the above-described embodiment, the example in which the drain materials 1, 1... Are embedded in the vertical direction has been described. However, the drain materials 1, 1. It may be.

  Further, the hole drilling device 5 used in the hole drilling step is not limited to the embodiment shown in the above-described embodiment. For example, the screw shaft disposed in the hole drilling rod 14 and the auger attached to the lower end of the screw shaft. A device comprising an excavation head such as a head is used to drill asphalt and excavated soil while discharging the drill shaft out of the drill rod 14 by rotation of the screw shaft, and penetrate the drill rod 14 into the ground A. It may be what was made.

A Ground B Existing paving section E New paving section
DESCRIPTION OF SYMBOLS 1 Drain material 2 Filter material 3 Reinforcement body 4 Cover member 5 Drilling device 6 Drain material embedding hole 10 Vehicle part 11 Boom 12 Guide shell 13 Drilling unit 14 Drilling rod 15 Pavement penetration part 16 Embedded hole main-body part 20 Protection member 21 Temporary paving material 22 Filling material 30 Horizontal drainage part 31 Crushed stone

Claims (4)

In the ground liquefaction prevention method that embeds a plurality of drain materials having water permeability in the ground below the pavement part up and down, and can suppress an increase in pore water pressure in the ground,
A drilling step of forming a drain material embedding hole that penetrates an existing pavement and reaches the desired depth of the ground, and the drain material is inserted into the drain material embedding hole and the drain is inserted into the ground A drain material burying step for burying a material and a temporary pavement step for closing the upper end opening of the drain material burying hole with a temporary pavement material are repeated, and a predetermined number of the drain materials are sequentially embedded in the ground under the existing pavement portion. After
A ground liquefaction prevention method characterized in that the existing pavement and temporary paving material are removed and a new pavement is constructed on the ground.   After removing the existing pavement, the surface portion of the ground is dug down to a desired depth, and thereafter, a horizontal drainage portion having water permeability is established so that the upper end of each drain material communicates with the new ground surface. The ground liquefaction prevention method according to claim 1, wherein the ground is formed and a new pavement is constructed on the horizontal drainage.   In the drilling step, the drain material embedding hole is formed by embedding a tubular drill rod in the ground, and in the drain material embedding step, the drain material is inserted into the drill rod, and then the drilling hole The ground liquefaction prevention method according to claim 1 or 2, wherein the drain material is embedded in the ground by pulling out a rod from the drain material embedding hole.   In the temporary paving step, a cylindrical protective member is installed on the inner periphery of the upper end of the drain material embedding hole so as to surround the periphery of the upper end of the drain material, and in this state, the upper end of the drain material embedding hole and the protective member The ground liquefaction prevention method according to claim 1, wherein the opening is closed with a temporary paving material.

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