JP3690432B2 - Structure foundation - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure foundation, especially flow for liquefaction of sandy soil due to earthquakes, also the structure foundation built in the ground by ground fluidization associated therewith to prevent displacement, from being damaged The present invention relates to a structure foundation provided with a pressure dispersion wall and a fluidization deterring wall .
[0002]
[Prior art]
There are many landfills in the coastal area where liquefaction may occur during an earthquake. Many of the expressways constructed in these landfills are three-dimensional in the form of continuous bridges in order to make effective use of land by using multiple layers of space. And most of the pier foundation as the bridge substructure is supported by the support layer by the pile foundation. For this reason, even if the foundation of a continuous bridge is constructed in a layer of sandy ground that may be liquefied during an earthquake (hereinafter referred to as the liquefied layer), its safety is sufficiently maintained. It has become.
[0003]
On the other hand, a large number of canals and other waterways are constructed in landfills near the river mouth for water transportation. For example, as shown in FIG. 6, the bridge girder 51 of the continuous bridge often straddles the water channel 52 orthogonally or obliquely. At this time, the pier foundation P that supports the bridge girder 51 straddling the water channel 52 is constructed relatively close to the water channel revetment. Naturally, this pier foundation P is also supported by the foundation pile 57 on the support layer 53 below the liquefied layer 54 (always indicated by a broken line).
By the way, when a large earthquake occurs and the loose sandy soil layer on which the pier foundation P is constructed is liquefied, the horizontal supporting force of the liquefied layer 54 is extremely reduced. At the same time, an excessive external force acts on the pile head 57a due to the inertial force acting on the bridge girder 51, the column 55 and the foundation footing 56, and the pile head 57a is plastically deformed. Moreover, when the earth and water pressure including the liquefaction pressure acts toward the revetment 60 on the side of the water channel that becomes an open surface in a state in which the horizontal supporting force of the ground is lost due to liquefaction, the structure of the revetment 60 resists the working earth and water pressure. It can no longer be done and protrudes to the waterway side. As a result, a phenomenon occurs in which the ground is laterally displaced from the land side toward the waterway side, and the foundation pile 57 and the foundation footing 56 of the pier foundation P are also displaced laterally by the lateral displacement of the ground (in this specification, This ground displacement phenomenon is hereinafter referred to as “ground fluidization” or simply “fluidization”).
[0004]
According to past investigations and studies, the permanent deformation of the pier foundation P damaged by the earthquake is due to the liquefaction caused by the plastic deformation of the foundation body during the earthquake, that is, the ground flow after the earthquake caused by the liquefaction. It is recognized that the influence of lateral displacement due to crystallization is dominant.
When the pier foundation P is located in the ground where the fluidization has occurred, the foundation footing 56 and the foundation pile 57 bear the fluidization pressure of the ground as shown in FIG. It is known that lateral displacement is suppressed. At this time, excessive fluidization pressure acts on the foundation pile 57, and a large horizontal force and rotational moment act on the plastically deformed pile head 57a. For this reason, a part of the foundation pile 57 in the ground is damaged, the displacement of the foundation is enlarged at the upper end of the column 55, and the bridge girder 51 is dropped from the scorpio (not shown). There is also a risk.
[0005]
Therefore, it has become necessary to urgently add a predetermined reinforcing structure to the existing pier foundation constructed in the ground where there is a risk of ground fluidization as described above. As countermeasures, there have been proposed a method of improving the ground of the pier foundation and the surrounding liquefaction range, and a method of surrounding the outer periphery of the pier foundation with an anti-earth pressure structure such as an underground continuous wall.
[0006]
[Problems to be solved by the invention]
However, in the case of countermeasure work by ground improvement, there is a problem that it is difficult to construct the existing bridge in the space under the girder, and the construction range is wide, so that the construction cost becomes high.
Measures to reinforce existing pier foundations with anti-earthquake structures such as underground continuous walls are also difficult to work in under-girder space of existing bridges, and there is a problem that wall construction costs are high.
[0007]
Therefore, the object of the present invention is to solve the problems of the conventional technology described above, disperse the earth pressure acting on the pier foundation by adding the inexpensive structure and fluidizing the ground via the foundation footing, The object of the present invention is to provide a structure foundation provided with a fluidization pressure dispersion wall and a fluidization deterring wall in order to reduce the burden on existing piles.
[0008]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the present invention has a lower end rooted up to a non-fluidized layer at the front surface position of an existing structure foundation where an open surface that causes ground fluidization is located on the back surface side of the ground, and the upper end is A fluidized pressure distribution wall which is located at a position corresponding to the height of the base plate of the structure foundation and is integrally constructed over substantially the entire width of the front surface of the structure foundation; A lower end is embedded in the support layer, and an upper end is located at a position corresponding to the height of the foundation plate, and includes a fluidization restraining wall integrally constructed along the fluidization direction of the structure foundation, in the upper end of the upper end and the fluidization deterring wall of the fluidizing pressure distribution wall is connected to the foundation plate by widening foundation plate Rukoto, among flow Ka圧acting on the fluidizing pressure distribution wall, the fluidizing pressure The fluidization pressure borne by the upper end of the dispersion wall is the widened base plate or the structure. It is transmitted to the fluidized deterring wall through the foundation, wherein the fluidizing pressure is to be supported by the fluidized deterring wall.
[0009]
The fluidizing pressure is transmitted to the foundation pile supporting the foundation structure, the tip of which is embedded in the support layer, and is shared and supported by the foundation pile and the fluidizing pressure suppression wall. It is preferable to do.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a structure foundation according to the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a perspective view showing the entire structure foundation constructed by adding to an existing pier foundation constructed near a waterway revetment. In the figure, a part thereof is cut out, and a fluid pressure transmission path is schematically added. As shown in FIG. 1, a widening footing 10 is added to the side surface of the existing foundation footing 2 on the foundation pile 1 of the pier foundation P. Further, a fluidizing pressure dispersing wall 11 is constructed on the front surface of the widened footing 10, and a fluidization inhibiting wall 12 is constructed on both side surfaces of the foundation footing 2 as a base plate. In addition, the foundation pile 1 of the pier foundation P penetrates the liquefied layer 6 and the non-fluidized layer 7, and the tip is embedded in the support layer 8. In addition, a water channel is located on the back side of the fluidizing pressure acting side, and a water channel revetment 9 is constructed as an open surface. As will be described in detail below, the fluidizing pressure acting upon the fluidization of the ground after the earthquake acts on the fluidizing pressure dispersion wall 11, and the fluidization deterring wall 12 and the foundation via the widening footing 10 and the foundation footing 2. It is transmitted to the pile 1. In this way, the load on the foundation pile 1 with respect to the fluidization pressure is greatly reduced, and the lateral displacement of the foundation footing 2 is sufficiently restrained by the fluidization restraining wall 12 having a large rigidity, and the displacement amount of the structure foundation is within the allowable value. Can be suppressed.
[0011]
Hereinafter, the structure of the structure foundation provided with the fluidization pressure dispersion wall and the fluidization suppression wall will be described with reference to FIGS. As shown in the plan view of FIG. 2, the foundation footing 2 of the existing pier foundation P is supported by 18 foundation piles 1. On the foundation footing 2, three reinforced concrete columns 3 are erected in a direction perpendicular to the bridge axis to support the beam 4. Further, a widening footing 10 is added so as to surround three side surfaces around the basic footing 2. The widening footing 10 is made of reinforced concrete, and a large number of joint bars (not shown) are connected to the side surface of the existing foundation footing 2 by chemical anchors or the like. Thereby, the widening footing 10 and the basic footing 2 are structurally integrated through the joint bar.
[0012]
A steel sheet pile wall as a fluidization pressure dispersion wall 11 is constructed on the land side front surface of the widening footing 10. This steel sheet pile wall is a wall body formed by connecting steel sheet piles 21 having a cross-sectional shape as shown in FIG. The cross section of the steel sheet pile 21 is H-shaped, the portion corresponding to the flange 21a is a straight steel sheet pile, the portion corresponding to the web 21b is a thick steel plate, and the flange 21a is a web made of thick steel plate. 21b is connected by welding. The section modulus of the steel sheet pile 21 alone is sufficiently larger than that of a steel pipe sheet pile having a diameter equal to the flange width.
[0013]
In order to construct this steel sheet pile 21, first, after cutting the periphery of the foundation footing 2 to the bottom of the foundation, before constructing the aforementioned widening footing 10, as shown in FIG. Install over a range. The tip is embedded in the non-fluidized layer 7 below the liquefied layer 6. As long as this tip is embedded to the non-fluidized layer 7, it does not have to penetrate to the support layer 8. It is preferable that the tip is embedded in the non-fluidized layer 7 to such an extent that the rotation of the wall body can be restricted when a load acts on the wall body. On the other hand, the upper end is securely fixed by the concrete of the widening footing 10 to be post-worked. For this reason, it is stopped in a state where a predetermined indentation length protrudes from the base bottom surface portion.
In addition, as the steel sheet pile 21 used for the fluidization pressure dispersion wall 11, various steel sheet piles 21 as shown in FIGS. 5B and 5C are used in addition to those shown in FIG. can do. In the steel sheet pile 21 shown in FIG. 2B, two thick steel plates corresponding to the web 21b are used. Thereby, wall body rigidity can be taken more largely than the figure (a). Moreover, as shown to the same figure (c), you may use the box-shaped steel sheet pile 21 which combined the U-shaped steel sheet pile. In addition, it is preferable to link the steel sheet pile 21 while connecting the length of the steel sheet pile 21 that can be constructed in the under-girder space.
[0014]
On the other hand, a known underground continuous wall as a fluidization deterring wall 12 is constructed on both side surfaces of the widening footing 10. The tip of the underground continuous wall reaches the support layer 8 having the same depth as the existing foundation pile 1 as shown in FIGS. Further, as shown in FIG. 2, the beam 4 receiving the bridge girder 5 projects to the position of the widening footing 10. For this reason, the excavator for wall construction cannot be installed in the space under the beam, and it is difficult to construct the wall at the beam position. Therefore, in the present embodiment, the wall body is divided into two parts, and the two wall bodies are constructed with a gap close to the beam width in one row. In addition, if it is a compact excavator which can be constructed in the space under the beam, it is preferable that the entire excavator constructs one underground continuous wall. In the present embodiment, the upper end of the continuous wall in each place is rigidly joined to the widening footing 10.
[0015]
Next, the role of the fluidization pressure dispersion wall 11 and the fluidization suppression wall 12 supported by the widening footing 10 will be described with reference to FIG.
In FIG. 1, the fluidization pressure acting on the fluidization pressure dispersion wall 11 is indicated by a white arrow. This fluidization pressure actually acts on the front surface of the fluidization pressure dispersion wall 11 over the entire height of the fluidization layer (corresponding to the liquefaction layer 6) as a trapezoidal distribution load according to the ground depth. The fluidizing pressure acting on the entire wall surface is shared and supported at the fulcrum positions 15 and 16 at the upper and lower ends. That is, each reaction force is distributed in the form of a horizontal strip at the upper end fulcrum 15 in the widened footing 10 and the lower end fulcrum 16 in the non-fluidized layer 7 below the liquefied layer 6. At this time, the reaction force shared by the lower end fulcrum 16 varies depending on the ground reaction force coefficient of the non-fluidized layer 7, but in this embodiment, the load sharing ratio between the upper end fulcrum 15 and the lower end fulcrum 16 is approximately 7: 3. ing. The fluidization pressure borne by the upper end fulcrum 15 is further transmitted to the fluidization suppression wall 12 and the existing foundation pile 1 through the foundation footing 2 and the widening footing 10 according to the rigidity ratio. It is preferable to set the section modulus of the fluidization inhibiting wall 12 so that the sharing ratio at this time is about 2: 1. In addition, the rebar cage built in the groove when constructing the underground continuous wall may be integrated by connecting the rebar cage while building it divided in the vertical direction so as not to interfere with the superstructure. .
[0016]
In the above explanation, a fluidization pressure dispersion wall and a fluidization deterrence wall are provided to be added to the existing pier foundation. It is possible to reduce the number of foundation piles by bearing more vertical support force.
It is also effective to apply this structure foundation to structures other than pier foundations, such as foundations for medium- and high-rise buildings constructed at the water's edge.
[0017]
【The invention's effect】
As is clear from the above description, according to the present invention, the displacement of the existing structure foundation constructed in the ground fluidization layer can be kept within the allowable value, and the superstructure such as a bridge girder by the fluidization of the ground can be achieved. Can be minimized.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a pier foundation as an embodiment of a structure foundation according to the present invention.
FIG. 2 is a plan view showing the pier foundation shown in FIG. 1 in plan view.
FIG. 3 is a side cross-sectional view showing the pier foundation shown in FIG. 1 along the line III-III.
4 is a front sectional view showing the pier foundation shown in FIG. 1 along the IV-IV sectional line. FIG.
FIG. 5 is a partial plan view showing a cross-sectional shape and a connected state of a single steel sheet pile constituting a fluidized pressure dispersion wall.
FIG. 6 is a state explanatory diagram showing a displacement state due to ground fluidization of a conventional pier foundation.
7 is a state explanatory view showing the displacement state shown in FIG. 6 in a plan view. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Foundation pile 2 Foundation footing 6 Liquefaction layer 7 Non-fluidization layer 8 Support layer 10 Widening footing 11 Fluidization pressure dispersion wall 12 Fluidization suppression wall

Claims (2)

At the front of the existing structure foundation where the open surface that causes ground fluidization is located on the back side of the ground, the lower end is rooted to the non-fluidized layer, and the upper end is the height of the foundation foundation of the structure foundation In the corresponding position, the fluidized pressure distribution wall integrally constructed over almost the entire width of the front surface of the structure foundation, and the lower end is rooted in the support layer on both sides of the structure foundation plate, and the upper end is A fluidization deterring wall that is in a position corresponding to the height of the foundation plate and is integrally constructed along the fluidization direction of the structure foundation;
Wherein at the upper end of the upper end and the fluidization deterring wall of the fluidizing pressure distribution wall is connected to the foundation plate by widening foundation plate Rukoto, among flow Ka圧acting on the fluidizing pressure distribution wall, the fluidization The fluidization pressure borne by the upper end of the pressure dispersion wall is transmitted to the fluidization suppression wall through the widened foundation plate or the structure foundation so that the fluidization pressure is supported by the fluidization suppression wall. A structural foundation characterized by The fluidizing pressure is transmitted to the foundation pile supporting the foundation structure, the tip of which is embedded in the support layer, and is shared and supported by the foundation pile and the fluidization pressure suppression wall. The structure foundation according to claim 1, wherein

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