JP2016000940A - Liquefaction countermeasure structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquefaction countermeasure structure that can reliably and effectively prevent occurrence of sand boiling and the like and that can more inexpensively and easily take countermeasures in a short period of time.SOLUTION: A liquefaction countermeasure structure B for reducing earthquake damage is provided in liquefaction ground G in which a ground surface part above a liquefaction layer 5 is provided with an impermeable or semipermeable covering layer 2. The liquefaction countermeasure structure B includes a plurality of drains 10 which are provided in a penetrating manner in ground G so as to communicate the liquefaction layer 5 with a permeable layer 1 between the liquefaction layer 5 and the covering layer 2 and/or the ground surface and which are arranged in a dotted pattern in a plan view.

Description

  The present invention relates to a structure for countermeasures against liquefaction for suppressing the crushed sand accompanying ground liquefaction and the progressive destruction of the ground to reduce damage caused by earthquakes.

  For example, in a liquefied ground where a sand layer of a non-liquefied layer is deposited on a stable non-liquefied layer, if liquefaction occurs in the liquefied layer due to an earthquake, the ground bearing capacity will disappear, Lateral flow or the like occurs, and there is a case where a large subsidence of the entire ground occurs over a wide area or a non-uniform subsidence occurs. For this reason, when constructing structures such as buildings on such liquefied ground, it is required to take measures against liquefaction.

  Conventionally, a technique for suppressing the occurrence of liquefaction by suppressing the ground area during an earthquake by compacting the ground or improving the ground in a lattice shape has been proposed and put into practical use. In recent years, there has also been proposed a floating type countermeasure that improves only the upper part of the liquefied layer and allows liquefaction of the lower part (see, for example, Patent Document 1).

  However, this type of countermeasure requires that the entire original ground be fully compacted over a wide area, or that the ground deformation during the earthquake should be reduced by earthquakes in order to prevent the occurrence of liquefaction. It requires a lot of cost. For this reason, there are many cases that are carried out limitedly just under the main structure, and it is applied to the entire ground in places with large areas such as parking lots and roads, in other words, places where large structures are not placed. Difficult to do.

  In addition, by installing an impervious covering member (covering layer) such as a floor slab or sheet on the surface layer so as to cover the entire ground, the ground when liquefaction has occurred while allowing liquefaction to occur Measures have been proposed to prevent the unevenness of the ground and the sand blowing to the ground surface (see, for example, Patent Document 2).

  However, even in this measure, it is necessary to form the covering member itself with sufficient rigidity in order to prevent the covering member itself such as the floor slab and the sheet from being uneven, and the cost is increased. Also, when liquefaction occurs, the surface structure itself may sink or float and tilt. Furthermore, there is a possibility that the sand blowing cannot be completely suppressed by the floor slab joint or the sheet joint.

  On the other hand, as shown in FIGS. 4 and 5, the inventor of the present application performs pavement (impermeable (non-permeable) coating layer) 2 on the gravel bed 1 to cover the surface portion. The liquefied ground G is excavated with a linear groove 3 at a predetermined interval, filled with gravel 4, and provided with a draining sand prevention structure (drainage) comprising a drain 6 configured to communicate the liquefied layer 5 with the ground surface. (Invention structure) A has been invented and a patent application has already been filed (see Patent Document 3).

  In this sandblast prevention structure A, when liquefaction occurs, water pressure can be released to the gravel layer (base course 1) or the ground surface through the drain 6, and the occurrence of sandblast can be prevented. Moreover, measures can be taken only by excavating the groove 3, filling the gravel 4 and laying the gravel layer 1, and an effective measure can be realized at low cost.

JP 2010-7381 A JP 2010-112039 A JP 2013-79544 A

  However, in the sand-sand prevention structure of Patent Document 3 by the inventor of the present application, it is possible to take measures at low cost, but it is necessary to excavate the ground in a linear shape to create a groove. For this reason, the construction range is also widened, and there is a possibility that the non-use period may be extended when applied to an external site or road that is already in service.

  In view of the above circumstances, the present invention provides a liquefaction countermeasure structure that can reliably and effectively prevent (suppress) the occurrence of sandblast and the like, and that can take measures quickly and easily in a short period of time. The purpose is to provide.

  In order to achieve the above object, the present invention provides the following means.

  The liquefaction countermeasure structure of the structure of the present invention is provided on a liquefied ground having an impermeable or hardly permeable coating layer on the surface portion above the liquefied layer, and is a liquid for reducing damage caused by an earthquake. It is a liquefaction countermeasure structure, and is pierced in the ground so as to communicate the liquefied layer, the water permeable layer between the liquefied layer and the coating layer, and / or the ground surface, and in a point shape in plan view. It is characterized by comprising a plurality of drains arranged.

  In the liquefaction countermeasure structure of the structure according to the present invention, it is desirable that the drain is formed by enlarging a portion located in the water permeable layer as compared with other portions.

  In the liquefaction countermeasure structure of the present invention, a liquefaction damage suppressing effect can be obtained by installing a drain in a spot-like (planar perspective) without providing a gravel groove as in the past. However, it is possible to suppress sand blowing at low cost and reliably prevent excessive unevenness and settlement.

  In addition, since spot-like measures can be taken, it is possible to minimize the closed section and period of construction for the exterior and road in service.

It is a sectional side view which shows the liquefaction countermeasure structure which concerns on one Embodiment of this invention. It is a top view which shows the liquefaction countermeasure structure which concerns on one Embodiment of this invention. It is a sectional side view which shows the example of a change of the liquefaction countermeasure structure which concerns on one Embodiment of this invention. It is a sectional side view which shows the conventional liquefaction countermeasure structure. It is a top view (plan sectional drawing) which shows the conventional liquefaction countermeasure structure.

  Hereinafter, a liquefaction countermeasure structure according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3.

  In the liquefaction countermeasure structure B of this embodiment, as shown in FIGS. 1 and 2, a non-liquefied layer 7 exists above the liquefied layer 5, and water permeability such as a roadbed is further above the non-liquefied layer 7. Damage (prevention) at the time of earthquake by providing on the liquefied ground G having the impervious layer (gravel layer) 1 and the impervious (hardly permeable) coating layer 2 such as pavement on the permeable layer 1 and the permeable layer 1 Is to do.

  In particular, the liquefaction countermeasure structure B of the present embodiment is for preventing the occurrence of sand sand by actively draining excess pore water from the liquefied layer 5 to the main part of the coating layer 2 when liquefaction occurs. is there.

  Here, the liquefied ground G in which the covering layer 2 such as pavement is present on the ground surface is against the sand even if liquefaction occurs due to the earthquake due to the covering layer 2 (pavement, roadbed, roadbed, etc.). Has some strength. Further, when there is a water-impermeable layer such as a viscous soil layer near the ground surface, this water-impermeable layer becomes the coating layer 2 and similarly exhibits the effect of suppressing the occurrence of sand sand.

  And in the liquefied ground G in which such a covering layer 2 exists, the sand pressure is generated at a portion where the weak sand is relatively weak, and the water pressure is intensively released from the sand sand hole by locally generating sand sand. In addition, there will be no damage such as depressions and large unevenness in the parts other than the sand hole. Further, when the covering layer 2 is formed by finishing the entire ground surface with uniform pavement or the like, it becomes impossible to specify a relatively weak point, so it is not possible to know where the sand is generated.

  On the other hand, in the liquefaction countermeasure structure B of the present embodiment, the liquefaction layer 5 and the liquefaction layer 5 and the coating layer 2 are between the liquefaction layer 5 and the liquefaction layer 5 between the liquefaction layer 5 and the coating layer 2 in consideration of effective use of the resistance against the sand blowing that the coating layer 2 has. The drain 10 is penetrated to the ground G so that the water permeable layer 1 and / or the ground surface may communicate with each other. Further, in the present embodiment, the plurality of drains 10 are arranged in a planar view at predetermined intervals.

Further, the drain 10 is formed by forming a drain hole 11 and filling a drain material 12. For example, the drain material 12 is made of a material that allows the drain 10 to have a high water permeability of 10 ⁻¹ cm / s or more and can prevent clogging due to sand intrusion during an earthquake. Specifically, it is preferable to use a gravel having a small particle size of about 5 mm or less as the drain material 12 or an industrial product drain material having performance equal to or higher than this.

  The drains 10 are basically formed at intervals of 10 m, and are installed at intervals of 5 to 20 m in consideration of various conditions such as the thickness of the coating layer 2 such as surface pavement and the non-liquefaction layer 7. The diameter and interval of the drain 10 may be set with reference to JP 2013-155558 A by the inventors of the present application.

  Further, the drain 10 needs to be formed so as to reach at least the upper end of the liquefied layer 5 and is preferably formed so as to penetrate the liquefied layer 5 by about 1 m. In the liquefaction countermeasure structure B of the present embodiment, since the ground G is allowed to liquefy, it is not necessary to place drains 10 in all layers of the liquefaction layer 5 as in the past countermeasures.

  Further, the drain 10 may have a uniform thickness up to the ground surface. However, as shown in FIG. 3, the drain 10 is used to reduce the pressure when draining to the ground surface, It is preferable to form the drain 10 by making the top end portion on the surface side larger (larger diameter) than other portions. In this case, it is preferable to set the cross-sectional area of the enlarged portion 13 at the top end portion as a guide at least twice the cross-sectional area of other portions.

  In addition, the drain 10 is preferably provided with a drainage treatment means 14 such as a drainage basin at the top end portion on the ground surface side so that the guided water can be smoothly drained to the ground surface and others.

  And in liquefaction countermeasure structure B of this embodiment which consists of the said structure, when liquefaction generate | occur | produces in liquefaction layer 5 by an earthquake, water is led from liquefaction layer 5 by drain 10, and it drains to the ground surface. Or escape to the water permeable layer 1. As the water in the liquefied layer 5 is drained through the drain portion in this way, the water pressure that has increased due to liquefaction slowly decreases. As a result, the sand, which is the ground material, does not come out on the ground surface, but subsidence due to liquefaction occurs, but subsidence, depression, and large unevenness due to sand and sand do not occur. It can be greatly reduced.

  Therefore, in the liquefaction countermeasure structure B of the present embodiment, a gravel groove is not provided, and a liquefaction damage suppressing effect can be obtained by spot-like countermeasures. It becomes possible to reliably prevent the occurrence of excessive unevenness and subsidence.

  In addition, since only spot measures are required on the surface layer, it is possible to minimize the closed section and period of construction for the exterior and road in service.

  As mentioned above, although one Embodiment of the liquefaction countermeasure structure which concerns on this invention was described, this invention is not limited to said one Embodiment, It can change suitably in the range which does not deviate from the meaning.

1 Roadbed (permeable layer such as gravel layer)
2 Pavement (impermeable or hardly permeable coating layer)
3 Groove 4 Gravel 5 Liquefaction layer 6 Conventional drain 7 Non-liquefaction layer 10 Drain 11 Drain hole 12 Drain material 13 Enlarged part 14 Waste water treatment means A Conventional liquefaction countermeasure structure (sand sand prevention structure)
B Liquefaction countermeasure structure G Liquefaction ground

Claims (2)

A liquefaction countermeasure structure for reducing damage caused by an earthquake, provided on a liquefied ground having a water impermeable or hardly water permeable coating layer on the surface portion above the liquefied layer,
A plurality of drains which are penetrated in the ground so as to communicate the liquefied layer, the water permeable layer between the liquefied layer and the coating layer, and / or the ground surface, and are arranged in the form of dots in plan view A liquefaction countermeasure structure characterized by comprising: In the liquefaction countermeasure structure according to claim 1,
A liquefaction countermeasure structure characterized in that the drain is formed by enlarging a portion located in the water-permeable layer as compared with other portions.

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