JP5878402B2 - Ground liquefaction countermeasure structure - Google Patents

Description

  The present invention relates to a ground liquefaction countermeasure structure suitable for the ground of an external part or the support ground of a light building.

  When building relatively large buildings such as condominiums and office buildings on the ground where the liquefied layer exists, for the main building, a support pile that reaches the support layer is built, or the support pile is built and compacted directly under the building. Sufficient liquefaction measures are often taken, such as building sand piles. On the other hand, since such liquefaction measures are expensive, the ground of exterior parts such as parking lots and light buildings (buildings other than relatively large buildings such as condominiums and office buildings) In many cases, sufficient countermeasures against liquefaction are not performed on the supporting ground of buildings (so-called No. 4 building) prescribed in Article 6, Paragraph 1, Item 4 of the Standard Law.

  One of the liquefaction measures that can be applied to exterior parts and the like is a gravel drain method. In the gravel drain method, a columnar body is formed in the ground by crushed stone with good water permeability, or a flat gravel mat is laid so as to communicate with the upper end of the columnar body. It is a method to dissipate.

  As a countermeasure against liquefaction by the same mechanism as the gravel drain method, instead of constructing crushed stone pillars, a drain pipe is buried in a vertical hole formed by driving a casing into the ground with a drilling machine, and water permeability is placed on the drain pipe. A drainage member that disperses pore water pressure during an earthquake by laying good crushed stones, and a drainage member that has a perforated pipe buried in the ground and a casing placed in the bottom plate of the perforated pipe, and a water-permeable material placed on the outer peripheral surface of the perforated pipe In the drainage structure, the upper end of the drain member is positioned in the tub and a cap is attached to the drain member so that a gap is formed, and the water overflowing from the gap is connected to the tub. A method of making it flow is known (Patent Document 1).

Japanese Patent Laid-Open No. 10-204864

  However, the conventional liquefaction countermeasure method may not prevent liquefaction when the input seismic motion exceeds the expected level. As a result, it cannot prevent uneven settlement of the ground surface. Therefore, even if it is an external part, for example, the parking lot will sink down and the vehicle will not be able to run, or the structure built in the external part will be damaged or tilted, etc. There is a risk that you will not be able to fulfill. Moreover, in the conventional gravel drain method, the drainage route of excess pore water has not been considered. It is conceivable to apply the technology of Patent Document 1 to drain excess pore water into the drainage ditch. However, if excess pore water exceeds the wastewater treatment capacity, excess pore water is ejected to the ground surface. Therefore, it is still impossible to prevent pavement damage, structure damage or tilting.

  The present invention has been made in view of such a background, and it is a first object of the present invention to provide a ground liquefaction countermeasure structure that can be constructed relatively inexpensively and easily and can prevent uneven settlement during an earthquake. And In addition, a second object of the present invention is to provide a ground liquefaction countermeasure structure in which the function as the ground is not lost even when the excess pore water pressure becomes high.

  In order to solve the above problems, the present invention is a liquefaction countermeasure structure (20) of the ground (10) where the liquefied layer (13) is present, and the target region (6 · 7) an improved ground layer (21) formed over the entire area, a horizontal drain layer (22) formed over the entire target area above the improved ground layer, connected to the horizontal drain layer and A plurality of vertical drains (24) formed substantially vertically so as to reach the liquefied layer and distributed in the target region, and provided on the surface of the target region, drain water flowing through the horizontal drain layer. It has a drainage groove (25), and excess pore water generated by liquefaction of the liquefied layer is caused to flow into the drainage groove via the vertical drain and the horizontal drain layer.

  By adopting such a configuration, excess pore water flowing into the vertical drain can be treated by the drainage ditch, allowing ground subsidence, but with the improved ground layer above the liquefied layer, the ground is not uneven. Settlement can be prevented. Moreover, since it can construct | assemble by adding an improved ground layer and a drainage ditch to the conventional gravel drain construction method, it can construct relatively inexpensively and easily. Therefore, it is suitable for the ground of an external part or a supporting ground of a light building, and when applied to the ground used as an external part or the like, it is possible to prevent the function from being lost when an earthquake occurs.

  Further, according to one aspect of the present invention, the surface of the target area is paved (23) over the entire area, the vertical drain is formed to reach the pavement, and the pavement has a hole (13a). It is possible to adopt a configuration in which a lid member (26) that is formed and opens in response to an increase in excess pore water pressure is attached to the hole.

  When the ground is paved, if excess pore water exceeds the drainage treatment capacity of the horizontal drain layer and drainage ditch, the excess pore water pressure in the horizontal drain layer increases and the excess pore water is As a result, the pavement is destroyed and the ground loses its function. However, with such a configuration, the lid member opens even if excess pore water exceeding the wastewater treatment capacity is generated. As a result, excess pore water can be ejected to the surface of the ground, and functional loss of the ground due to pavement damage can be prevented.

  Further, according to one aspect of the present invention, the horizontal drain layer (22) includes a crushed stone layer (22A) and a drain pipe (22B) embedded in the crushed stone layer, and one end of the drain pipe is the vertical pipe. It is set as the structure provided corresponding to the said vertical drain so that it may connect to a drain (24) and an other end may connect to the said drainage groove (25A).

  By adopting such a configuration, the drainage treatment capacity of the horizontal drain layer can be improved and the excess pore water can be prevented from being ejected to the ground surface, so that even if a large excess of pore water is generated, the function of the ground is lost. Can be prevented.

  Moreover, according to one aspect of the present invention, the vertical drain can include a crushed stone columnar body (24A) or a water permeable tube (24B).

  According to this configuration, it is possible to appropriately select a crushed stone columnar body or a water permeable tube as a vertical drain according to the state of the ground, and to construct a liquefaction countermeasure structure with optimum performance at low cost.

  As described above, according to the present invention, it is possible to construct relatively inexpensively and easily, to prevent uneven settlement during an earthquake, and to prevent the liquid from being lost even when the excess pore water pressure becomes high. Can be provided.

Plan view of the liquefaction countermeasure structure according to the first embodiment II-II sectional view in FIG. Enlarged view of the main part in FIG. The perspective view which shows the example of the cover member shown in FIG. Explanatory drawing of the construction procedure of the liquefaction countermeasure structure which concerns on 1st Embodiment Sectional drawing of the liquefaction countermeasure structure which concerns on 2nd Embodiment

  Hereinafter, some embodiments of the liquefaction countermeasure structure 20 according to the present invention will be described in detail with reference to the drawings.

<< First Embodiment >>
As shown in FIG. 1, in addition to the apartment 2, a light building such as a bicycle parking lot 3, an electrical room 4, and a garbage storage 5 is constructed on the site 1. On site 1, tile pavement is applied to the entrance of the apartment 2 and the approach portion 6 connected to the bicycle parking lot 3, and the parking lot 7 is provided with asphalt pavement. As shown in FIG. 2, the site 1 is a liquefied ground 10 where a liquefied layer 13 exists, and a non-liquefied layer 12, a liquefied layer 13, and a non-liquefied layer 14 are deposited in this order above the support layer 11. doing.

  Here, the liquefaction countermeasure structure 20 is constructed with the ground used as the approach section 6 and the parking lot 7 in the site 1 as a target area. The liquefaction countermeasure structure 20 for each target area (approach part 6 and parking lot 7) is an improvement formed by improving the upper part of the non-liquefied layer 14 over the entire area of the target area above the liquefied layer 13. The ground layer 21, the horizontal drain layer 22 formed over the entire target region above the improved ground layer 21, and the pavement 23 formed on the surface of the liquefied ground 10 above the horizontal drain layer 22. It is configured by stacking.

  In addition, vertical drains 24 that are dispersedly arranged at a predetermined interval in plan view are formed in the target region of the liquefied ground 10, and drainage grooves 25 are formed at a predetermined interval on the surface of the target region.

  The liquefied layer 13 is made of water-containing sandy soil, and the water that has been saturated between the sand grains flows due to vibration during an earthquake, and the intergranular bond between the sand grains is broken to behave like a liquid. The layer that loses. When the liquefied layer 13 is liquefied, the water pressure of the fluidized pore water rises rapidly, and excess pore water is generated.

  The non-liquefaction layer 14 is a layer that does not liquefy during an earthquake. On the other hand, the improved ground layer 21 is a shallow improved ground layer obtained by improving a relatively shallow ground (for example, a non-liquefied layer 14 of 2 m from the ground surface) near the ground surface. For example, a powder-based or slurry-based solidified material is used. It is formed by stirring and mixing the non-liquefied layer 14, compacting by rolling and solidifying. The non-liquefaction layer 14 and the improved ground layer 21 become the roadbed of the approach unit 6 and the parking lot 7.

  The vertical drain 24 is for draining the excess pore water of the liquefied layer 13 generated at the time of an earthquake upward. Here, the vertical drain 24 is composed of a crushed stone column (gravel drain) 24A, connected to the horizontal drain layer 22 and It is formed substantially vertically so as to reach the liquefied layer 13. In addition, it is good to use the single-grain crushed stone with many voids and high drainage capacity for crushed stone. The vertical drain 24 only needs to reach the liquefied layer 13 at the lower end, but here has a length that enters the liquefied layer 13 and reaches the lower surface of the liquefied layer 13.

  The horizontal drain layer 22 is a layer for draining the excess pore water of the liquefied layer 13 discharged upward by the vertical drain 24 in the horizontal direction, and here is constituted by a crushed stone layer (gravel mat) 22A. As for the crushed stone, single-grain crushed stone having a large gap and high drainage capacity may be used similarly to the vertical drain 24. The horizontal drain layer 22 becomes the roadbed of the approach unit 6 and the parking lot 7.

  The pavement 23 of the approach unit 6 is a water-permeable type in which a sand cushion is laid on the horizontal drain layer 22 and blocks and tiles are laid on the side drain layer 22 and the joints are filled with sand. On the other hand, the pavement 23 of the parking lot 7 is a non-permeable asphalt pavement and covers the horizontal drain layer 22 in a watertight manner.

  As shown in FIG. 3, the drainage groove 25 includes a water-permeable U-shaped groove 25 </ b> A having a depth at which the bottom surface 25 a of the groove is lower than the upper surface of the horizontal drain layer 22, and the bottom surface 25 a of the groove is a horizontal drain. There is a water-permeable L-shaped side groove 25 </ b> B that is higher than the upper surface of the layer 22. The U-shaped groove 25A has water permeability (porous concrete) on the bottom wall and both side walls. When the water level of excess pore water becomes higher than the bottom surface 25a of the groove, the water flowing through the horizontal drain layer 22 is U-shaped. It flows into the groove 25A and is drained. On the other hand, the bottom wall of the L-shaped side groove 25B has water permeability, and when the water pressure of excess pore water flowing through the horizontal drain layer 22 increases by the thickness of the bottom wall of the L-type side groove 25B, excess pore water Flows into the L-shaped side groove 25B and is drained.

  A hole 23a is formed at an appropriate position in the pavement 23, and a lid member 26 that opens according to an increase in excess pore water pressure is attached to the hole 23a. The hole 23a and the lid member 26 are disposed at a position corresponding to the vertical drain 24 in which the drainage groove 25 is not provided immediately above. Since the vertical drain 24 and the horizontal drain layer 22 are made of the same crushed stone and both are connected and there is no boundary, it can be said that the hole 23a and the lid member 26 are provided at the upper end of the vertical drain 24.

  As shown in FIG. 4A, for example, the hole 23a and the lid member 26 provided in the pavement 23 are manhole-shaped lids composed of a cylindrical frame 27 defining the hole 23a and a lid member 26 attached to the cylindrical frame 27. The assembly 28 can be installed on the horizontal drain layer 22 and the surroundings can be installed by asphalt paving. Alternatively, as shown in FIG. 4B, the hole 23a may be directly formed in the pavement 23 by die cutting or core removal, and the lid member 26 fitted to the hole 23a may be fitted. In any case, the lid member 26 is detached from the hole 23a with a water pressure smaller than the water pressure at which the pavement 23 is damaged by the excess pore water pressure in the horizontal drain layer 22, so that the excess pore water can be ejected from the hole 23a.

  Next, the construction procedure of the liquefaction countermeasure structure 20 will be described with reference to FIG. As shown to (A), using the construction machine 31 with respect to the liquefied ground 10 in which the support layer 11 (FIG. 2), the non-liquefied layer 12, the liquefied layer 13, and the non-liquefied layer 14 deposited in this order. The upper part of the non-liquefied layer 14 is improved and the improved ground layer 21 is formed by performing a shallow layer mixing process in which the solidified material is stirred and mixed, and compacted by rolling and solidified. At this time, if it is necessary to form the horizontal drain layer 22 below the U-shaped groove 25A, this portion is excavated before the improved ground layer 21 is solidified.

  Next, as shown in (B), a dedicated machine 33 having a casing pipe 32 is installed on the improved ground layer 21 so as to reach the non-liquefiable layer 12, that is, to penetrate the liquefied layer 13. By inserting the casing pipe 32 into the liquefied ground 10 and pulling out the casing pipe 32 while supplying crushed stone from the tip of the casing pipe 32, the vertical hole formed by the casing pipe 32 is filled with crushed stone, and the shape of the crushed stone column A vertical drain 24 composed of the body 24A is constructed.

  After all the vertical drains 24 are constructed, as shown in (C), while installing the U-shaped groove 25A and the L-shaped side groove 25B (FIG. 3), the crushed stones are spread on the improved ground layer 21 from the crushed stone layer 22A. The horizontal drain layer 22 is constructed. Finally, as shown in (D), asphalt pavement is applied on the horizontal drain layer 22 to construct the pavement 23 on the surface of the liquefied ground 10, and the holes 23a are formed at positions corresponding to the vertical drains 24 of the pavement 23. The liquefaction countermeasure structure 20 is constructed by providing the lid member 26 with the cover.

  By configuring the liquefaction countermeasure structure 20 in this way, excess pore water generated by liquefaction of the liquefied layer 13 during an earthquake flows into the vertical drain 24 as shown by arrows in FIG. After rising, it moves in the horizontal direction through the horizontal drain layer 22 and flows into the drainage groove 25, and is drained by the drainage groove 25. Thereby, in the liquefied ground 10, the liquefied layer 13 condenses and sinks at the time of liquefaction, but the uneven subsidence does not occur because the improved ground layer 21 exists above the liquefied layer 13. Moreover, since the liquefaction countermeasure structure 20 can be constructed by adding an improved ground layer 21 and a drainage groove 25 to the conventional gravel drain construction method, it can be constructed relatively inexpensively and easily. Therefore, it is suitable also for the area | region used as exterior parts, such as the approach part 6 and the parking lot 7, in the site 1 of the liquefied ground 10, and it can prevent that the parking lot 7 etc. lose its function at the time of the occurrence of an earthquake. .

  Moreover, an inexpensive non-permeable asphalt can be used as the pavement 23 of the parking lot 7. Even when the horizontal drain layer 22 is covered with the pavement 23 in a water-tight manner as described above, the lid member 26 is provided on the pavement 23, so that the degree of liquefaction is large and the drainage of the horizontal drain layer 22 and the drainage groove 25 is performed. Even when excess pore water exceeding the treatment capacity is generated, the lid member 26 is detached and the excess pore water is ejected from the holes 23a. Therefore, the pavement 23 is not damaged and the function as the approach portion 6 or the parking lot 7 in the target area is not lost.

<< Second Embodiment >>
Next, a second embodiment of the present invention will be described with reference to FIG. In addition, the description about the structure, procedure, and effect similar to the first embodiment is omitted. In the present embodiment, a perforated pipe 24B is used as the vertical drain 24 instead of the crushed stone columnar body 24A, and a drain pipe 22B embedded in the crushed stone layer 22A substantially horizontally as the horizontal drain layer 22 in addition to the crushed stone layer 22A. Is used. The drain pipe 22B is provided with respect to the vertical drain 24 without the drain groove 25 immediately above, and is disposed at the lower part of the crushed stone layer 22A and connected to the perforated pipe 24B through the joint 29. It is inserted into a through hole 25b formed in the side wall and connected to the U-shaped groove 25A. The drain pipe 22B is made of, for example, a vinyl chloride pipe, and may be a pipe having no holes or a perforated pipe. In the case of using a perforated pipe, it is possible to use a tube in which holes are formed only in the upper half at the time of installation. By adopting such a configuration, an excess gap can be obtained only when a large amount of excess pore water flows. Water leaks to the horizontal drain layer 22, and when the excess pore water pressure is low, it can be immediately drained to the U-shaped groove 25A. The perforated pipe 24B of the vertical drain 24 extends further upward from the joint 29 and reaches the pavement 23, and a lid member 26 is attached to the upper end thereof.

  Even if the liquefaction countermeasure structure 20 is configured in this way, excess pore water generated in the liquefaction layer 13 flows into the perforated pipe 24B, rises up the vertical drain 24, and then flows into the drain pipe 22B. It moves horizontally along the horizontal drain layer 22 and is treated by the drainage grooves 25. Further, when crushed stone is used for the vertical drain 24 and the horizontal drain layer 22, clogging is likely to occur due to the inflow of muddy water generated when the liquefied layer 13 is liquefied. Since the drainage pipes 22B are used for the horizontal drain layers 22, clogging is less likely to occur, so that the durability of the liquefaction countermeasure structure 20 can be improved (the number of times of liquefaction is increased).

  This is the end of the description of specific embodiments, but the present invention is not limited to these embodiments. For example, in the above embodiment, the liquefaction countermeasure structure 20 is constructed for the liquefied ground 10 in which the non-liquefied layer 14 is deposited on the liquefied layer 13. It can also be applied to the ground where the layer 13 exists. In this case, the improved ground layer 21 may be formed by subjecting the upper part of the liquefied layer 13 to a shallow layer mixing process. Moreover, in the said embodiment, although the liquefaction countermeasure structure 20 is applied with respect to the approach part 6 and the parking lot 7, you may apply to the ground of light buildings, such as the bicycle parking lot 3 and the electrical room 4. FIG. Moreover, in the said embodiment, although the drainage groove 25 is provided above the vertical drain 24, you may provide the drainage groove 25 in the position away from the vertical drain 24 by planar view.

  On the other hand, in the said 2nd Embodiment, although the drainage pipe 22B is used for the horizontal drain layer 22, the perforated pipe | tube 24B of the vertical drain 24 is used for the horizontal drain layer 22 which consists of the crushed stone layer 22A, without using the drainage pipe 22B. It can also be set as the form which connects (the upper end of the perforated pipe | tube 24B rushes into the crushed stone layer 22A). Furthermore, in the said 2nd Embodiment, although the perforated pipe | tube 24B is used for the vertical drain 24, as long as it is a water-permeable permeable pipe, you may use the pipe | tube which consists of porous concrete, for example. Moreover, in the said 2nd Embodiment, it is also possible to set it as the form which uses 24 A of crushed stone columnar bodies of 1st Embodiment as the vertical drain 24. FIG.

  On the other hand, in the existing parking lot 7 or the like, the liquefaction countermeasure structure 20 may be constructed on the ground where the improved ground layer 21 is formed and the crushed stone layer 22A is provided on the improved ground layer 21. it can. In this case, the existing crushed stone layer 22A may be used as the horizontal drain layer 22, the vertical drain 24 may be constructed, and the lid member 26 may be installed. In addition, the specific shape, arrangement, material, and order of construction procedures of each member can be changed as appropriate without departing from the spirit of the present invention. Moreover, all the components and construction procedures of the liquefaction countermeasure structure 20 according to the present invention shown in the above embodiment are not necessarily indispensable, and can be appropriately selected.

6 Approach section (target area)
7 Parking lot (target area)
10 Liquefaction ground 13 Liquefaction layer 20 Liquefaction countermeasure structure 21 Improved ground layer 22 Horizontal drain layer 22A Crushed stone layer 22B Perforated pipe (permeable pipe)
23 Pavement 23a Hole 24 Vertical drain 24A Crushed stone pillar 24B Perforated pipe 25 Drainage groove 25A U-shaped groove (drainage groove)
25B L-shaped side groove (drainage groove)
26 Lid member

Claims (3)

The liquefaction countermeasure structure of the ground where the liquefaction layer exists,
An improved ground layer formed over the entire area of interest above the liquefied layer;
A lateral drain layer formed over the entire target area above the improved ground layer;
Pavement applied over the entire surface of the target area;
A plurality of vertical drains connected to the horizontal drain layer and leading to the pavement and formed substantially vertically so as to reach the liquefied layer, and distributed in the target region;
A drainage groove provided on the surface of the target area, for draining water flowing through the horizontal drain layer ,
A lid member attached to a hole formed in the pavement ,
Excess pore water generated by liquefaction of the liquefied layer is caused to flow into the drainage groove through the vertical drain and the horizontal drain layer, and the lid member is opened in response to an increase in excess pore water pressure. Ground liquefaction countermeasure structure characterized by that. The horizontal drain layer includes a crushed stone layer and a drain pipe embedded in the crushed stone layer,
2. The ground according to claim 1 , wherein the drain pipe is provided corresponding to the vertical drain so that one end is connected to the vertical drain and the other end is connected to the drain groove. Liquefaction countermeasure structure. The ground liquefaction countermeasure structure according to claim 1 or 2 , wherein the vertical drain includes a crushed stone columnar body or a water permeable tube.

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