JP4325225B2 - Projection amount calculation method for shunt structure in fluidization countermeasure method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a construction method for reducing damage due to ground liquefaction during an earthquake and the like, and a method for calculating a protrusion amount of a shunt structure used for the method.
[0002]
[Prior art]
Lateral flow due to ground liquefaction during earthquakes and the like can cause significant damage to structures with foundation piles. FIG. 7 shows the operation, wherein 1 is a foundation footing embedded in the ground, and 2 is a plurality of pile foundations that support the foundation footing 1. When the lateral flow A occurs due to the ground liquefaction, the footing 1 is pushed by the fluid force, and when the shear strength of each pile 2 is exceeded, each pile 2 breaks and, as indicated by the broken line, downstream in the flow direction. It will fall to the side and move or be buried with the foundation footing 1, causing serious damage.
[0003]
Therefore, conventionally, the following method has been considered.
(1) Improve the ground to prevent liquefaction of the ground itself.
(2) Reduce fluidity.
(3) Produces cross-sectional performance that does not break even when subjected to fluid force. Each method is proposed.
[0004]
However, in the method (1), a considerably wide ground improvement is required with respect to the foundation construction range, the construction range is widened, and the construction cost is high. In some cases, the scope of improvement cannot be secured due to site boundaries.
The method (2) is conventionally difficult to quantitatively evaluate, and the degree of damage reduction cannot be clearly shown.
Furthermore, in the method (3), it is necessary to considerably increase the strength of the pile supporting the foundation, which also causes the construction cost to increase.
[0005]
In addition, there is a construction method in which two shunt walls are arranged in a boat shape on the upstream side of the liquefaction flow direction with respect to the foundation structure, and a pair of side walls that surround the side portion of the foundation structure are formed continuously with these shunt walls (patent) Reference 1). This construction method is a kind of the method (2), in which the fluid force is not directly applied to the foundation by surrounding the fluid force with a flow dividing wall.
[0006]
[Patent Document 1]
JP-A-9-49244 [0007]
[Problems to be solved by the invention]
However, since the construction method disclosed in the above-mentioned document requires a protective body surrounding the foundation, a large site is required. In addition, since fluid force acts on the entire protective body, it must be structured to counteract this, and the creation cost is high.
[0008]
Furthermore, in general, the flow direction due to ground liquefaction is the direction from the mountain side to the sea side, and the directionality is determined according to the topography, but if the landform changes due to landfill, the flow direction changes. In some cases, it is difficult to deal with such cases.
[0009]
The present invention solves the above problems, the purpose of which is to reduce the flow force against the foundation due to ground liquefaction at the time of earthquake by bringing the flow resistance reduction effect to the foundation itself, and damage to the pile foundation and there is provided a projection amount calculation method for diversion structure in fluidized measures construction method that allow reducing the damage caused by this.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the method for calculating the amount of protrusion of the shunt structure in the fluidization countermeasure method of the present invention calculates the fluid force of the ground where the foundation footing is placed, and the limit value of the strain or sectional force of the pile foundation. And calculating a necessary fluid force reduction rate from the ratio between the calculated fluid force and the calculated limit value, and the amount of lateral protrusion from the foundation footing of the shunt structure and the thickness of the foundation footing. The relationship between the ratio and the fluid force reduction rate is determined, and by using this relationship, the ratio of the lateral protrusion amount from the shunt structure and the footing thickness so that the required fluid force reduction rate can be obtained. It is characterized by calculating .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1-3 show the case where this invention construction method is applied to the existing foundation.
[0017]
In FIG. 1A, an existing foundation footing 10 is constructed in the ground and supported by a plurality of pile foundations 12. In addition, the upper half part in the ground is the liquefied layer E1, and the lower half part is the non-liquefied layer E2, and the case where the liquefied layer E1 reaches the pile 12 is illustrated.
[0018]
In the fluidization countermeasure method for the existing foundation footing 10 described above, first, the surface facing it according to the direction of the lateral flow is excavated as shown in FIG. This excavation depth is set to a height that reaches the non-liquefied layer E2, and anchor bars 14 are arranged on the exposed side surfaces of the foundation footing 12, and then, at this position, as shown in FIG. 16 is arranged. The mold 16 has a substantially triangular shape in both the longitudinal section and the plane, the top of the triangle is directed in the lateral flow direction, the bottom of the vertical direction reaches the top surface of the basic footing 10 and the non-liquefied layer E2, and further in the left-right direction. It is a quadrangular pyramid-shaped member whose bottom is equal to the width of the foundation footing 10, and is produced as an FRP throwing mold at a factory, for example, and installed on the side surface facing the lateral flow.
[0019]
Thereafter, concrete is cast into the mold 16 and fixed integrally to the side surface of the foundation footing 10 and then backfilled as shown in FIG.
[0020]
In the above configuration, when the lateral flow A is generated toward the shunt structure 18 as shown by the arrows in FIGS. 2 and 3 due to the earthquake and the accompanying liquefaction, the lateral flow A is separated. Since the fluid flows along the inclined surface of the flow dividing structure 18 while being distributed vertically and horizontally from the top of 18 and the flow force is diverted to the foundation footing 10 by the flow, the flow pressure against the foundation footing 10 becomes extremely small, This prevents movement of the foundation footing from being buried and damage to the pile 12 due to the crystallization phenomenon.
[0021]
Next, FIG. 4 shows a second embodiment when the liquefied layer E1 is up to the depth of the foundation footing 10, and the length of the bottom in the vertical direction of the flow dividing structure 18 is set equal to the thickness of the foundation footing 10. ing. Although not shown, the length of the bottom in the left-right direction is the same as the width dimension of the foundation footing 10.
[0022]
Further, FIG. 5 shows a third embodiment, and in this embodiment, a case where the flow dividing structure 18 is arranged around the four sides of the basic footing 10 is shown. In this embodiment, the lateral flow direction due to liquefaction is not specified, or the structure can cope with lateral flow in all directions in response to future topographic changes.
[0023]
In each of the above embodiments, the fluidization countermeasure method for the existing foundation footing 10 has been described. However, a structure in which the shunt structure 18 is added to the foundation footing 10 from the beginning even at the time of new construction.
[0024]
Further, in installing the above flow dividing structure 18, the longer the projecting length of the flow dividing structure 18, the lower the flow pressure against the foundation footing 12, but this requires a sufficient site area and is uneconomical. On the other hand, if the pile foundation 12 is distorted or a flow pressure exceeding the limit value of the cross-sectional force is applied, there is no point in adding the shunt structure 18.
[0025]
Therefore, when the shunt structure 18 is installed, the projecting amount is designed as follows.
(1) Acquire in advance the amount of flow displacement of the relevant ground: Calculate according to the existing guidelines (may be unnecessary for the guidelines for calculating the fluid force).
(2) Calculate the spring during an earthquake: Calculate the ground force of the non-liquefied layer and the liquefied layer, and multiply the spring constant by the flow displacement of (1) to calculate the fluid force. In the case of a guideline that can evaluate the fluidity, calculate the fluidity directly.
(3) Setting of critical fluid force: Set the limit value of strain or section force of pile foundation.
(4) Set the fluid force reduction rate: The ratio of (2) and (3) is the required reduction rate.
(5) Determining the streamline shape relationship between the reduction rate and the shunt structure 18: the ratio between the protrusion amount a of the shunt structure 18 and the thickness b of the foundation footing 10 shown in FIG. Calculate b / a required for (4) from the relationship with the line shape. This relationship is shown in FIG .
[0026]
In the figure, for example, when b / a is 2: 1, if the rigidity of the non-liquefied layer is soft, the fluid force reduction rate is close to 1, and if the rigidity of the non-liquefied layer is normal, the reduction ratio is Is lower than this, and when the non-liquefied layer has a rigid rigidity, the reduction rate is even lower.
[0027]
Therefore, while estimating the protrusion amount a with respect to the thickness b according to the fluid force reduction rate, and setting the range below the limit fluid force that is less than the limit value of the strain of the pile or the cross-sectional force, the shunt current that becomes the optimum reduction rate The amount of protrusion of the structure can be calculated. That is, the optimal protrusion amount of the shunt structure can be obtained by grasping the geology, pile strength, etc. of the liquefied ground where the foundation footing is arranged in advance.
[0028]
In the actual reduction rate measurement, the resistance load of the square resistor placed in various viscous fluids and the shunt structure with an appropriate amount of protrusion attached thereto was compared and measured by model experiments. Easy to calculate. Furthermore, in this embodiment, the cross-section and the plane are a quadrangular pyramid shape that is a straight triangle. However, if a more preferable streamline can be found by a model experiment or the like, it is desirable to adopt such a shape.
[0029]
As is clear from the above explanation, according to the present invention, in determining the protruding amount of the shunt structure in the fluidization countermeasure construction method, it is quantitative by knowing in advance the geology of the liquefied ground, pile strength, etc. The optimal protrusion amount can be calculated .
[Brief description of the drawings]
FIGS. 1A to 1F are cross-sectional views showing a creation procedure according to a first embodiment of the construction method of the present invention.
FIG. 2 is a sectional view showing the completed state.
FIG. 3 is a plan view of the same.
FIG. 4 is a cross-sectional view showing a second embodiment of the present invention.
FIG. 5 is a cross-sectional view showing a third embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the flow force reduction rate and the ratio of the protrusion amount / basic footing thickness of the shunt structure, and a schematic cross-sectional view showing the ratio.
FIG. 7 is a schematic cross-sectional view showing a problem when a lateral fluid force is generated in the conventional foundation footing due to ground liquefaction during an earthquake.
[Explanation of symbols]
10 Foundation footing 12 Pile foundation 18 Dividing structure a Projecting amount b of dividing structure Thickness of foundation footing

Claims (1)

Calculate the flow force of the ground where the foundation footing is located, calculate the limit value of the strain or section force of the pile foundation, and reduce the required fluid force from the ratio of the calculated flow force and the calculated limit value set the rate, and the ratio between the thickness of the side projecting amount and foundation footing from basic footing of the shunt structure, indexing the relationship between the flow force reduction factor, by using this relationship, the required flow force A method for calculating a protrusion amount of a shunt structure in a fluidization countermeasure method , wherein a ratio between a lateral protrusion amount from the shunt structure and a footing thickness so as to obtain a reduction rate is calculated.

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