JP3807190B2 - Foundation construction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a foundation construction method, and more particularly to a construction method for economically constructing a foundation using a suction load.
[0002]
[Prior art]
There are various methods for building a foundation of a building structure. For example, a foundation construction method using a steel pipe sheet pile is known as a method employed when building a foundation in water.
[0003]
In the foundation construction method using steel pipe sheet piles, a plurality of steel pipe sheet piles are placed adjacent to each other in the horizontal direction through the joints in the bottom of the bottom, and the bottom of the ground is surrounded by a steel pipe sheet pile in a closed shape. Then, a base part is formed, and then an upper structure part such as a leg part or a superstructure is constructed above the base part.
[0004]
In such a foundation construction method, the steel pipe sheet pile at the foundation has been placed so that its lower end reaches a complete support layer in order to safely support the upper load and the like. However, for example, when the depth of the complete support layer is deep and incomplete in the middle, but there is a soil layer with a strength that can be regarded as a support layer, there has been a technical problem described below.
[0005]
[Problems to be solved by the invention]
That is, in the above-described conventional foundation construction method, the steel pipe sheet pile is driven to a deep support layer, so that the steel pipe sheet pile becomes long, so that the joint portions compete and can be driven to a predetermined depth. Difficult to build foundations.
[0006]
Moreover, in order to make sure that the support layer is firmly rooted, there is a risk of damaging the sheet pile by placing it more than necessary, and it takes a lot of time for placing and the construction period is also long.
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a foundation construction method capable of shortening the construction period while avoiding the difficulty of construction. There is.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, the base portion surrounding the ground in a closed planar shape is positioned at the upper side of the complete support layer having a lower N value greater than 50 and an N value of 20 Is formed so as to reach a deemed support layer that is smaller than 30 and formed on the upper side of the base portion, and a bottom plate portion that closes its upper end is formed, and thereafter, a leg portion and an upper portion are formed on the bottom plate. In the construction method of the foundation for constructing the upper structure part such as a work, after the bottom plate is formed, the water in the foundation part is forcibly drained to add a load corresponding to the upper load applied to the foundation part. In addition, the ground in the foundation was subsidized in advance.
According to the foundation construction method constructed in this way, after the bottom slab is formed, the water in the foundation is forcibly drained to add a load corresponding to the overload applied to the foundation, and the ground in the foundation As the ground sinks, the foundation including the bottom plate sinks by an amount corresponding to the loading load.
Therefore, even if an upper structure portion such as a leg portion or an upper work is subsequently constructed on the bottom plate, the entire structure does not sink and the structure is stabilized.
Since such a stable structure can be constructed without incorporating the lower end of the base portion into the complete support layer, it is possible to reduce the construction cost and the construction period. The said base part can be comprised from the some steel pipe sheet pile connected mutually through a coupling part.
According to this structure, since it is not necessary to drive the lower end of the steel pipe sheet pile of the foundation part to the complete support layer, the casting can be performed easily, in a short time, and without being damaged.
The foundation portion can be formed of an underground continuous wall that connects and forms panels with each other via a joint portion.
According to this structure, since it is not necessary to form the lower end of the underground continuous wall of a foundation part to a complete support layer, each panel length of an underground continuous wall can be shortened.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment of a foundation construction method according to the present invention. The foundation construction method shown in the figure is a case where the present invention is applied to construction of an underwater foundation.
[0009]
In the construction method of the underwater foundation of the present embodiment, a plurality of steel pipe sheet piles 12 are used for the foundation portion 10. The plurality of steel pipe sheet piles 12 are driven into the bottom ground 14 while being sequentially connected in the horizontal direction via joints, and have a planar shape such as a circle, an ellipse, or a polygon that closes the bottom bottom ground 14. Go.
[0010]
In this case, the lower end of each steel pipe sheet pile 12 to be cast in the bottom ground 14 reaches the deemed support layer 18 located on the upper side of the complete support layer 16 located at a large depth of the bottom ground 14. To cast.
[0011]
The full support layer 16 is a formation having an N value greater than 50, and the deemed support layer 18 is a formation having an N value greater than 20 and less than 30. The existence depth is confirmed by the drilling survey.
[0012]
In the steel pipe sheet pile 12 placed in the closed planar shape, drain pipes 19 are appropriately arranged at the locations. This drain pipe 19 extends along the longitudinal direction of the steel pipe sheet pile 12 over the entire length thereof to the inner surface side of the steel pipe sheet pile 12, and is an opening in which a filter material that prevents intrusion of earth and sand is fixed on the inner surface of the tip. Is provided.
[0013]
After the steel pipe sheet pile 12 is placed and the foundation 10 is formed, the filter layer 20 is formed by digging up the water bottom ground 14 of the portion surrounded by the steel pipe sheet pile 12 and filling it with crushed stone or the like. Then, underwater concrete is cast on the upper part to form the leveling layer 22, and then the bottom plate 24 made of reinforced concrete is formed on the upper side of the leveling layer 22.
[0014]
The bottom plate 24 is formed in a disc shape so that the outer peripheral edge is fixed to the inner surface of the steel pipe sheet pile 12 and the upper end of the base portion 10 made of the closed planar steel pipe sheet pile 12 is closed.
[0015]
When the bottom plate 24 is formed, the first drainage passage 25 that connects the upper end side of the drainage pipe 19 and the second drainage passage that communicates with the filter layer 20 through the leveling layer 22 at the lower end side. 26 is formed inside.
[0016]
Here, in the case of the present embodiment, since the bridge pier portion 28 which is integrally provided is constructed at substantially the center portion of the bottom plate 24, the upper side of the first and second drainage passages 24 and 26 is The bridge pier 28 extends in the vertical direction and extends to the upper end thereof.
[0017]
In the case of the present embodiment, since the pier portion 28 is constructed in advance in the center portion of the bottom plate 24, the drainage passages 24 and 26 are installed therein. It is not necessary to construct such a pier portion 28 in advance, and only the bottom plate 24 may be constructed.
[0018]
When the bottom slab 24 and the pier 28 are formed as described above, a suction-type suction device such as a vacuum pump is connected to the upper ends of the first and second drainage passages 25 and 26 so as to close the planar base portion 10 that is closed. Thus, the water in the bottom ground 14 whose side surfaces are separated and whose upper ends are separated by the bottom plate 24 is forcibly drained.
[0019]
In this forced drainage, a deep part is performed through the drain pipe 19, and a surface and a shallow part is performed through the filter layer 20. The submerged ground 14 is mainly consolidated and sinks. In this consolidation, water moves from the lower side of the opening on the lower end side of the drainage pipe 19 along with the suction drainage of water, so that the ground below the drainage pipe 19 also has pore water. It drains and sinks.
[0020]
The subsidence amount in this case is set on the assumption that the upper structure portion 34 including the pier portion 28 and the upper work 30 such as a bridge girder is constructed on the bottom plate 24. That is, when the total load (upload) of the bottom plate 24 and the upper structure 34 is applied to the water bottom ground 14, the amount that the ground above the support layer 16 sinks is preliminarily determined based on the properties of the ground. The amount is set to be approximately the same as the amount of subsidence, and the amount corresponding to that amount is preliminarily subsidized.
[0021]
In addition, if the water bottom ground 14 surrounded by the base portion 10 is forcibly drained, the pressure in this portion is reduced, and a suction load corresponding to the water depth pressure is applied on the bottom plate 24. According to the subsidence of the submarine ground 14, it will gradually settle.
[0022]
When the above-described pre-sinking or subsidence is performed by a preset amount, forced drainage is stopped, and an upper work 30 such as a bridge girder is constructed on the upper end side of the pier 28.
[0023]
Now, according to the construction method of the foundation configured as described above, after the bottom plate 24 is formed, the upper load applied to the foundation portion 10 by forcibly draining the water in the foundation portion 10, that is, the bottom plate 24. Since the ground 14 in the foundation portion 10 is preliminarily subtracted by adding the total load of the upper structure portion 34 and the upper structure portion 34, the foundation portion 10 sinks by an amount corresponding to the overlay load with the subsidence of the ground 14. .
[0024]
Therefore, even if the upper structure portion 34 such as the pier portion 28 and the upper work 30 is subsequently constructed on the bottom plate 24, the entire settlement is avoided and the structure is stabilized.
[0025]
Since such a stable structure can be constructed without the lower end of the base portion 10 being embedded in the complete support layer 16, it is possible to reduce the construction cost and the construction period.
[0026]
More specifically, in the case of the present embodiment, the base portion 10 is composed of a plurality of steel pipe sheet piles 12 that are connected to each other via a joint portion, so that the lower end of the steel pipe sheet pile 12 is a complete support layer. Since it is not necessary to drive up to 16, it is possible to perform driving easily, in a short time, and without damage.
[0027]
FIG. 2 shows another embodiment of the basic construction method according to the present invention. The same or corresponding parts as those in the above embodiment are designated by the same reference numerals and the description thereof is omitted. Only will be described.
[0028]
In the embodiment shown in the figure, the base portion 10 a is composed of an underground continuous wall 40. The underground continuous wall 40 is formed so as to surround the ground 42 in a closed planar shape by sequentially connecting rectangular panels to each other in the horizontal direction.
[0029]
The underground continuous wall 40 is constructed to a depth at which the lower end reaches the deemed support layer 16. When the underground continuous wall 40 is constructed, a drain pipe 19a that penetrates through the inside and opens to the side surface on the lower end side is installed.
[0030]
A plurality of drain pipes 19a are arranged along the circumferential direction of the underground continuous wall 40 at a predetermined interval. When the underground continuous wall 40 is constructed, the inner peripheral surface and the outer peripheral surface on the upper end side thereof are integrated, and the bottom plate 24a that closes the upper end of the underground continuous wall 40 is formed.
[0031]
When the bottom plate 24a is formed, a first drainage passage 25a that connects the upper end side of the drainage pipe 19a is embedded therein. The first drainage passage 25a extends in the up-down direction through a bridge pier 28a erected at the center of the bottom plate 24a.
[0032]
When the bottom slab 24a and the pier portion 28a are formed, the groundwater in the ground 42 surrounded by the underground continuous wall 40 is forcibly drained through the first drainage passage 25a and the drainage pipe 19a.
[0033]
When such forced drainage is performed, as in the above-described embodiment, the consolidated ground 42 is consolidated and subsidence occurs, and a suction load is also applied. Settling as in the example.
[0034]
The amount of sedimentation in this case is set in advance in consideration of the overload as in the above embodiment. Even in the foundation construction method constructed as described above, the same effects as the above embodiment can be obtained, and in the case of this embodiment, the lower end of the underground continuous wall 40 of the foundation portion 10a is fully supported. Since it is not necessary to form up to the layer 16, each panel length of the underground continuous wall 40 can be shortened.
[0035]
【The invention's effect】
As described above in detail in the embodiment, according to the foundation construction method according to the present invention, the construction period can be shortened while avoiding the difficulty of construction.
[Brief description of the drawings]
FIG. 1 is a cross-sectional explanatory view of a construction state showing a first embodiment of a foundation construction method according to the present invention.
FIG. 2 is a cross-sectional explanatory view of a construction state showing a second embodiment of the foundation construction method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10,10a Foundation part 12 Steel pipe sheet pile 14 Submarine ground 16 Complete support layer 18 Deemed support layer 28, 28a Bridge pier part 30 Superstructure 34 Superstructure 40 Underground continuous wall

Claims (3)

The base part surrounding the ground in the closed planar shape is positioned on the upper side of the complete support layer having an N value larger than 50 , and the N value is larger than 20 and smaller than 30. Formed to reach,
On the upper side of the base part, a bottom plate part for closing the upper end is formed,
After this, on the bottom slab, in the construction method of the foundation to build the upper structure part such as legs and superstructure,
After the bottom plate is formed, by forcibly draining the water in the foundation portion, a load corresponding to the upper load applied to the foundation portion is applied to pre-sink the ground in the foundation portion. Foundation construction method.   The foundation construction method according to claim 1, wherein the foundation portion includes a plurality of steel pipe sheet piles connected to each other via a joint portion.   The foundation construction method according to claim 1, wherein the foundation portion is an underground continuous wall that connects and forms panels with each other via a joint portion.

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