JP2017193867A - Liquefaction countermeasure structure of construction and design method of liquefaction countermeasure structure of construction - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquefaction countermeasure structure of construction and a design method of liquefaction countermeasure structure of construction capable of effectively preventing (reducing) damage due to liquefaction without requiring large area or volume.SOLUTION: A construction 15 is configured to reduce damage due to liquefaction on a construction 4 which is constructed including a pile foundation 3 in the ground G which has a non-liquefaction layer 2 on a liquefaction layer 1. The construction includes a spacer member 16 formed enclosing the pile foundation 3, with an upper end part of which is disposed in a non-liquefaction layer 2 on the liquefaction layer 1 and a lower end part of which is disposed in a non-liquefaction layer 5 under the liquefaction layer 1. The spacer member separates the liquefaction layer 1 at the pile foundation 3 side from the liquefaction layer 1 outside thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a structure liquefaction countermeasure structure for reducing damage caused by liquefaction of a structure including a pile foundation, and a design method of the liquefaction countermeasure structure of the structure.

  When the ground G having the non-liquefied layer 2 on the liquefied layer 1 is liquefied during an earthquake, for example, as shown in FIG. 13, the ground G above the liquefied layer 1 (the upper non-liquefied layer 2). ) Is greatly displaced. For example, as shown in FIG. 14, when a structure (building) 4 having a pile foundation (pile) 3 is constructed on such ground G, liquefaction occurs during an earthquake and the ground displacement changes suddenly. The pile 3 may be damaged at the boundary between the liquefied layer 1 and the upper non-liquefied layer 2, and the boundary between the liquefied layer 1 and the non-liquefied layer 5 below the liquefied layer 1.

  Conventionally, in order to prevent the damage of the pile 3 (damage of the structure 4) due to the liquefaction of the ground G, the ground is improved so as not to liquefy the ground G, or the pile 3 is reinforced and liquefied. Many measures have been used to withstand the generated load F. However, in the countermeasures by the ground improvement, in particular, when the liquefied layer 1 is continuously present up to the deep part or there are a plurality of liquefied layers 1 with the non-liquefied layer interposed therebetween, the lowermost liquefied layer 1 is When it exists in the deep part etc., since it was necessary to improve the ground G of a huge volume, there existed a problem that the cost of countermeasures became very expensive. Moreover, there was a problem that it was difficult to adopt measures for ground improvement and measures for reinforcing the pile 3 to the existing pile foundation structure 4.

  On the other hand, as shown in FIG. 15, for example, a countermeasure for liquefaction is proposed in which a base material 4b of the structure 4 (upper structure 4a) is filled with a material softer than the liquefied layer 1 (soft material 6). (For example, refer to Patent Document 1). In this measure, the force F acting on the structure 4 during liquefaction is absorbed by the soft material 6 to reduce the influence on the structure 4.

  Further, for example, as shown in FIG. 16, a liquefaction countermeasure is proposed in which a lightweight material 7 is embedded around the structure 4 (upper structure 4a). In this measure, the influence on the structure 4 is reduced by reducing the passive resistance due to ground displacement during liquefaction.

  Further, as shown in FIG. 17 (FIG. 17A: sectional view, FIG. 17B: plan view), the ground G around the structure 4 (upper structure 4a) is replaced with wall-shaped sand 8. Measures to prevent liquefaction have been proposed. In this measure, the wall-like sand 8 that has been replaced is liquefied to suppress the ground displacement at the time of liquefaction and reduce the influence on the structure 4.

  Furthermore, there is a measure for providing a wall along the outer periphery of the structure 4, a so-called skirt wall construction method. In this skirt wall construction method, for example, as shown in FIG. A connected rigid wall (skirt wall 10) is provided to reduce the horizontal load of the pile 3 (see, for example, Patent Document 2).

JP 2000-178997 A Japanese Unexamined Patent Publication No. 57-9925

  However, in the measure for filling the soft material 6 into the root portion 4b of the structure 4, the ground G around the root portion 4b becomes soft, so that the swing of the structure 4 (upper structure 4a) is caused by the root portion 4b. The suppression effect will be reduced. For this reason, at the time of a small and medium earthquake that does not cause liquefaction, the stress of the pile 3 may increase due to the shaking of the structure 4 and may be damaged.

  Further, in the measure for embedding the lightweight material 7 around the structure 4, it is necessary to embed the lightweight material 7 in a large area in order to surely reduce the passive resistance due to the ground displacement at the time of liquefaction. was there.

  Even in the measure to replace the ground G around the structure 4 with the sand 8, the groundwater level T needs to be near the ground surface in order to surely liquefy the wall-like sand 8, and under what conditions Even the lower structure 4 is not applicable, and there is a problem that there is a great limitation in its use.

  In the skirt wall construction method, a rigid wall (skirt wall 10) connected to the foundation 4c is used to reduce the horizontal load of the pile 3 by bearing a horizontal force. It is not intended to reduce the horizontal force acting on 4 or the pile 3. That is, the skirt wall 10 is provided to reduce the shearing force acting on the joint portion between the foundation 4c of the structure 4 and the pile 3 and to reduce damage to the joint portion, and has no relation to liquefaction. (It is not provided as a countermeasure against liquefaction). Further, when such a skirt wall 10 is in the non-liquefied layer 2 on the liquefied layer 1, there is a possibility that the load (horizontal force) acting on the structure 4 is increased instead of liquefying. Moreover, there is a possibility that pile stress generated at the boundary between the liquefied layer and the lower non-liquefied layer located deeper than the lower end of the skirt wall 10 cannot be reduced.

  In view of the above circumstances, the present invention provides a structure for preventing liquefaction of a structure that can effectively prevent (reduce) damage due to liquefaction without requiring a large area and volume, and liquid of the structure. The purpose is to provide a design method of the countermeasure structure.

  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 a structure for reducing damage caused by liquefaction of a structure constructed with a pile foundation on a ground having a non-liquefied layer on a liquefied layer. The upper end side is arranged on the non-liquefied layer above the liquefied layer, and the lower end side is arranged on the non-liquefied layer below the liquefied layer. An edge cutting member is provided for cutting the liquefied layer on the pile foundation side and the liquefied layer on the outside thereof.

  Further, in the structure for preventing liquefaction of a structure according to the present invention, the displacement of the edge cutting member obtained by applying the ground displacement at the time of earthquake in the absence of the structure to the structure model having the edge cutting member via a ground spring. It is desirable that the pile foundation stress is obtained by giving to the pile foundation as ground displacement, and the specifications of the pile foundation are set based on the stress of the pile foundation.

  Furthermore, in the liquefaction countermeasure structure for a structure according to the present invention, it is more desirable that the edge cutting member is set in consideration of only the rigidity of the surface orthogonal to the direction of the seismic force.

  The structure liquefaction countermeasure structure design method of the present invention is a method for designing a liquefaction countermeasure structure of any one of the above structures, and is a structure specification setting for setting the specifications of the structure. A ground spring setting step of calculating a ground spring of the pile foundation, the edge cutting member, and a base portion of the structure, and calculating a ground displacement at the time of an earthquake when there is no structure as a general ground displacement Based on the ground displacement calculation step and the ground displacement of the portion located in the edge cutting member of the pile foundation, the general ground displacement is given to the structure model via the ground spring to calculate the displacement of the edge cutting member. An edge cutting member internal ground displacement calculating step for obtaining a ground displacement inside the edge cutting member at the time of an earthquake, and applying the general ground displacement to the edge cutting member and the base of the structure; and Border cutting Applying the ground displacement inside the material to the pile foundation to obtain the ground displacement inside the new edge cutting member to obtain the ground displacement inside the edge cutting member, and the edge displacement member inner ground displacement updating step of the edge cutting member displacement It is repeated until the difference converges, and the edge displacement member ground displacement determination step for determining the displacement of the edge shearing member at the stage where the difference in displacement of the edge shearing member converges as the ground displacement inside the edge shearing member; A pile stress calculating step of calculating a stress at the time of the earthquake of the pile foundation based on the ground displacement inside the edge cutting member determined in the ground displacement determining step.

  According to the structure liquefaction countermeasure structure and the structure liquefaction countermeasure structure design method of the present invention, the ground displacement during earthquake during liquefaction is large, and the pile stress at the boundary between the liquefied layer and the non-liquefied layer. The pile stress can be significantly reduced by providing the edge-cutting member even for a structure such as a building in which the remarkably increases.

It is sectional drawing which shows the liquefaction countermeasure structure of the structure which concerns on one Embodiment of this invention. It is a flowchart which shows the design method of the liquefaction countermeasure structure of the structure which concerns on one Embodiment of this invention. It is the figure used for description at the time of calculating general ground displacement in the design method of the liquefaction countermeasure structure of the structure concerning one embodiment of the present invention. It is the figure used for description at the time of calculating the ground displacement inside an edge cutting member in the design method of the structure liquefaction countermeasure structure concerning one embodiment of the present invention. It is the figure used for description at the time of calculating the ground displacement inside an edge cutting member in the design method of the structure liquefaction countermeasure structure concerning one embodiment of the present invention. It is the figure used for description at the time of calculating the ground displacement inside an edge cutting member in the design method of the structure liquefaction countermeasure structure concerning one embodiment of the present invention. It is the figure used for description at the time of calculating the ground displacement inside an edge cutting member in the design method of the structure liquefaction countermeasure structure concerning one embodiment of the present invention. It is the figure used for description at the time of calculating the ground displacement inside an edge cutting member in the design method of the structure liquefaction countermeasure structure concerning one embodiment of the present invention. It is the figure used for description at the time of calculating the ground displacement inside an edge cutting member in the design method of the structure liquefaction countermeasure structure concerning one embodiment of the present invention. It is a figure which shows the model used in verification experiment. It is a figure which shows the accommodation state of the model insulation member (wall material) used in verification experiment. It is a figure which shows the result of a demonstration experiment, (a) is a bending moment which arises in a pile foundation, (b) is a figure which shows the shear force which arises in a pile foundation. It is a figure which shows the displacement at the time of liquefaction of the ground which has a non-liquefied layer on a liquefied layer. It is the figure used for description regarding the damage of the structure by liquefaction. It is sectional drawing which shows the conventional countermeasure against liquefaction of a structure. It is sectional drawing which shows the conventional countermeasure against liquefaction of a structure. It is sectional drawing and a top view which show the conventional countermeasure against liquefaction of a structure. It is sectional drawing which shows the conventional countermeasure against liquefaction of a structure.

  Hereinafter, a structure liquefaction countermeasure structure and a structure liquefaction countermeasure structure design method according to an embodiment of the present invention will be described with reference to FIGS. 1 to 13. The present embodiment relates to a structure for preventing or reducing damage to a structure (pile foundation structure) during liquefaction, and a method for designing the structure.

  First, as shown in FIG. 1, the structure 4 according to the present embodiment is constructed on the ground G having the non-liquefied layer (upper non-liquefied layer) 2 on the liquefied layer 1. It is constructed by supporting the upper structure 4a with a plurality of piles (pile foundation 3). Further, the upper structure 4a is constructed by rooting the lower end side (rooting part 4b) into the upper non-liquefied layer 2.

  And the liquefaction countermeasure structure 15 of the structure of this embodiment includes the liquefaction layer 1 on the side of the plurality of piles 3 (in this embodiment, the liquefaction layer 1 immediately below the structure 4) and the liquefaction layer 1 on the outside thereof. The edge cutting member 16 is provided in the ground G on the outer side in the horizontal direction of the structure 4. Moreover, the edge cutting member 16 of this embodiment is continuously provided along the outer periphery of the structure 4, and is provided in the liquefied layer 1 by rooting the lower end part 16a side.

  Further, the edge cutting member 16 has an upper end portion 16b disposed in the upper non-liquefied layer 2 and a lower end portion 16a disposed on the non-liquefied layer (lower non-liquefied layer) 5 below the liquefied layer 1. Rooted in.

Note that the edge cutting member 16 need not be particularly limited in its rigidity, material, thickness, and the like. Moreover, as long as it arrange | positions so that the liquefied layer 1 in which the pile 3 was provided may be enclosed, it may be partially discontinuous, or it may be partially cut out and a hole. The edge cutting member 16 may be any member that does not allow the permeation of the soil as much as possible even when water is passed during liquefaction of the ground.
In the present embodiment, the edge cutting member 16 is provided so that the upper end portion 16 b side thereof is in contact with the root insertion portion 4 b of the structure 4. On the other hand, the edge cutting member 16 may be provided with its upper end disposed in the upper non-liquefaction layer 2. At this time, it is more preferable that the upper end portion of the edge cutting member 16 is disposed above the lower end of the structure 4. Further, the edge cutting member 16 is provided with a gap between the root insertion portion 4b, or by improving the ground between the root insertion portion 4b, and is provided with an intervening layer between the root insertion portion 4b. Also good.

  Furthermore, the structure 4 of this embodiment acts on the pile foundation 3 with the liquefaction of the liquefied layer 1 at the time of an earthquake by providing the edge cutting member 16 (structure liquefaction countermeasure structure 15) as described above. Stress is obtained as shown in FIG. 2, and a pile foundation 3 is constructed based on the obtained stress (specifications such as the shape, proof stress, and rigidity of the pile foundation 3 are set).

  First, as shown in FIG. 2 (and FIG. 1), specifications such as the shape of the pile 3 and the edge-cutting member 16 and the strength, rigidity, etc. of each member (and as a whole) are set (Step 1: structure specification setting). Process). In addition, pile springs, edge cutting member springs (wall springs), root insertion springs, that is, ground springs at the roots of the piles 3, edge cutting members 16, and structures 4 are calculated / set (Step 2: ground spring setting step).

  Further, as shown in FIG. 2 and FIG. 3 (and FIG. 1), the ground displacement at the time of earthquake (hereinafter referred to as general ground displacement) in the absence of the edge cutting member 16 (liquefaction countermeasure structure 15) is calculated (Step 3: General Ground displacement calculation process).

  As shown in FIGS. 2, 4, 5, and 6 (and FIG. 1), the ground displacement of the portion located in the edge cutting member 16 of the pile 3 is set to 0 (based on the reference), and the general ground displacement is set to the ground. The displacement of the edge cutting member 16 is calculated by giving it to the structure model via the spring, and the obtained displacement of the edge cutting member 16 is set as the internal ground displacement surrounded by the edge cutting member 16 (Step 4, Step 5: Ground in the edge cutting member) Displacement calculation step).

  Further, in this embodiment, as shown in FIGS. 2, 4, 5, 6, 7, 8, 8, and 9 (and FIG. 1), general ground displacement is applied to the edge cutting member 16 and the root insert 4b. Then, the ground displacement in the edge cutting member 16 is given to the pile 3 and the ground displacement in the new edge cutting member 16 is calculated (Step 6: ground displacement updating process in the edge cutting member). This operation is repeated until the difference in displacement of the edge cutting member 16 converges. Then, the edge-cutting member displacement at the stage where the difference in displacement of the edge-cutting member 16 converges is defined as the edge-cutting member internal ground displacement (Step 7, Step 8: edge cutting member internal ground displacement determining step).

  That is, since the deformation of the edge cutting member 16 is undecided in the initial stage, in this embodiment, the deformation of the edge cutting member 16 and the ground deformation applied to the pile are made equal by repeated calculation or the like, and the displacement at this time is set in the edge cutting member. Determined as ground displacement.

  Furthermore, in this embodiment, in order to evaluate on the safe side, the rigidity of the edge cutting member 16 is set in consideration of only the rigidity of the surface orthogonal to the direction of the seismic force (the edge cutting member 16 that causes out-of-plane deformation).

  Next, the pile stress considering the inertial force and the ground displacement is calculated based on the determined ground displacement within the edge cutting member (Step 9: pile stress calculating step). At this time, for example, the pile stress is obtained by a simple sum or square sum of the pile stress due to the building inertia force and the ground displacement, or the pile stress is obtained by simultaneously loading the inertia force and the ground displacement.

Here, a demonstration experiment will be described in which a sine wave having a period of 1 second, a steady 30 waves, and a maximum acceleration of 100 cm / s ² is used as an input wave of ground motion in actual conversion.

In this demonstration experiment, the experimental model shown in FIG. 10 was used.
The earth tank used a sheared soil layer of 800 mm × 400 mm × 325 mm. The lower non-liquefied layer 5 of the ground G is a No. 3 silica sand layer having a relative density of about 100% and a thickness of 100 mm (actual conversion 3 m), and the liquefied layer 1 and the upper non-liquefied layer 2 are No. 7 having a relative density of 50%. A silica sand layer was created by the air drop method. The pore fluid was silicon oil having a specific gravity of 1 and a viscosity of 30 cs, and the groundwater level was 70 mm from the ground surface (2.1 m in actual conversion).

  The pile 3 was made of four brass pipes having a diameter of 12 mm, a thickness of 0.5 mm, and a length of 252 mm (pitch interval 96 mm). The pile tip was pinned using a bearing. The pile head can be regarded as a rigid joint.

  The base was made of aluminum having a flat surface of 150 mm × 164 mm and a thickness of 40 mm. In order to prevent the inertia of the structure from prevailing, the structure was limited to the foundation part, and the weight of the structure was reduced so that the specific gravity of the structure was kept almost equal to the surrounding ground.

  The edge cutting member (wall material) 16 is an aluminum plate having a thickness of 0.3 to 4.0, and the tip is inserted into urethane so that vibration from the bottom of the earth tub is not propagated. In addition, the edge cutting member 16 is a Teflon (registered trademark) tape (0.08 mm thick, five plate-like members each having a width of 29 to 36 mm so that the bending rigidity around the vertical axis does not contribute to the result. Hereinafter, it was prepared by bonding with Teflon tape). In order to eliminate the influence of the in-plane rigidity of the side wall, as shown in FIG. 11, a 1 mm gap is provided between the side wall and the front and rear wall (adjacent edge cutting members 16), and a Teflon tape having a thickness of 0.08 mm is used. I just kept it. The pile 3 and the edge cutting member (excluding the thickness of 0.3 mm) 16 were attached with strain gauges on 7 cross sections.

  Main model specifications and similarity rules are shown in Table 1.

  In addition, the experimental cases are as shown in Table 2, C0 without the edge cutting member 16, and C0.3, C1.0, C2.0, C4, and C4 with the thickness changed in the range of 0.3 to 4.0 mm. A total of 5 cases were set. Table 2 also shows the ratio of the bending rigidity of the edge cutting member 16 to the bending rigidity of the retaining wall in which H-shaped steels of H400-200-8-13 are arranged at a pitch of 900 mm. That is, C0.3 uses the edge cutting member 16 having a very small bending rigidity and a rigidity ratio of less than 1 / 10,000 of the retaining wall.

  FIG. 12 is a result of the proof experiment, and the bending moment distribution (FIG. 12A) and the shear force distribution (FIG. 12) at the time (about 12.6 s) when the maximum bending moment is exhibited at the liquefied layer boundary immediately after liquefaction. 12 (b)).

  From these results, it was confirmed that the presence of the edge cutting member 16 reduces the bending moment and the shearing force near the upper and lower boundaries of the pile head and the liquefied layer 1 to about 2/3 to 1/2. Moreover, there was almost no difference in the effect by the thickness of the edge cutting member 16, and it was confirmed that even if it is a very thin edge cutting member 16, the stress reduction effect of the pile 3 by the ground displacement at the time of an earthquake is large.

  In other words, it was important for the function / action of the edge cutting member 16 to prevent slipping of the liquefied ground, and it was confirmed that the difference in effect due to the difference in rigidity was small. That is, it is confirmed that the edge cutting member 16 may be a very thin member or a member having low rigidity as long as it can prevent the liquefied ground from slipping through, and can exhibit an excellent pile stress reduction effect regardless of the rigidity. It was done.

  Therefore, in the design method of the structure liquefaction countermeasure structure 15 and the structure liquefaction countermeasure structure 15 of the present embodiment, the ground displacement at the time of earthquake during liquefaction is large, and the liquefaction layer 1 and the non-liquefaction layer 2 For the structure 4 such as a building where the pile stress is remarkably increased at the boundary with 5, it is possible to significantly reduce the pile stress by providing the edge cutting member 16.

  In the above, one embodiment of the structure liquefaction countermeasure structure and the structure liquefaction countermeasure structure design method according to the present invention has been described. However, the present invention is not limited to the above embodiment, and Changes can be made as appropriate without departing from the spirit of the invention.

  For example, the edge cutting member 16 may be installed when the structure 4 is constructed (for example, a retaining wall may be used as the edge cutting member 16), or a sheet pile is driven into the ground G as the edge cutting member 16, and the existing structure 4 Alternatively, the edge cutting member 16 (liquefaction prevention structure 15) may be added.

1 Liquefaction layer 2 Upper non-liquefaction layer 3 Pile (pile foundation)
4 Structure 4a Superstructure 4b Rooting part 4c Foundation 5 Lower non-liquefied layer 6 Soft material 7 Light weight material 8 Sand 10 Skirt wall (wall, wall)
15 Structure liquefaction countermeasure structure 16 Edge cutting member F Horizontal force (load)
G Ground T Groundwater level

Claims (4)

A structure for reducing damage caused by liquefaction of a structure constructed with a pile foundation on the ground with a non-liquefied layer on the liquefied layer,
It is provided so as to surround the pile foundation, and the upper end side is arranged on the non-liquefied layer above the liquefied layer, and the lower end side is arranged on the non-liquefied layer below the liquefied layer. A liquefaction countermeasure structure for a structure, comprising an edge cutting member provided to cut off the liquefaction layer on the pile foundation side and the liquefaction layer on the outside thereof. In the structure against liquefaction of a structure according to claim 1,
By applying the displacement of the edge cutting member obtained by applying the ground displacement at the time of earthquake without the structure to the structure model having the edge cutting member through a ground spring as the ground displacement, A structure for liquefaction countermeasures for a structure, wherein stress is obtained and the specifications of the pile foundation are set based on the stress of the pile foundation. In the structure for preventing liquefaction of a structure according to claim 1 or 2,
The structure for preventing liquefaction of a structure, wherein the rigidity of the edge cutting member is set considering only the rigidity of a surface orthogonal to the direction of seismic force. A method for designing a liquefaction countermeasure structure for a structure according to any one of claims 1 to 3,
A structure specification setting step for setting the specifications of the structure;
A ground spring setting step for calculating a ground spring of the base portion of the pile foundation, the edge cutting member and the structure;
A general ground displacement calculating step of calculating the ground displacement at the time of earthquake when there is no structure as a general ground displacement;
The displacement of the edge cutting member is calculated by applying the general ground displacement to the structure model via the ground spring while calculating the displacement of the edge cutting member while taking the ground displacement of the portion located in the edge cutting member of the pile foundation as a reference. The ground displacement calculation process in the edge cutting member to obtain the ground displacement inside the edge cutting member at the time of the earthquake,
An edge cutting member which gives the ground displacement inside the edge cutting member by giving the general ground displacement to the edge cutting member and the base of the structure, and giving the ground displacement inside the edge cutting member to the pile foundation. Inland ground displacement update process,
The edge cutting member inner ground displacement update process is repeated until the difference in displacement of the edge cutting member converges, and the displacement of the edge cutting member at the stage where the difference in displacement of the edge cutting member converges is regarded as the ground displacement inside the edge cutting member. Determining the ground displacement in the edge cutting member to be determined; and
A pile stress calculating step of calculating a stress at the time of the earthquake of the pile foundation based on the ground displacement inside the edge cutting member determined in the edge displacement member ground displacement determining step. Design method for liquefaction countermeasures.

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