JP2004211502A - Foundation reinforcing structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foundation reinforcing structure for improving limit bearing power, allowing reinforcement to initial rigidity, reducing a structural scale, and reducing an excavation quantity by reinforcing the ground itself. <P>SOLUTION: This foundation reinforcing structure is provided with shearing resistance piles 2 and 2 so as to penetrate through a sliding breakdown surface of a foundation structure 1 in a lower side ground area of an installation surface and/or an outside ground area of the installation surface of the foundation structure. Compacting reinforcing piles 3 and 3 for compacting the ground are arranged in an adjacent ground area around the foundation structure. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a foundation reinforcing structure capable of increasing the ultimate support force of a direct foundation type such as an installed caisson or solid foundation by reinforcing the ground itself.
[0002]
[Prior art]
Generally, the foundation structure is roughly divided into a shallow foundation such as a footing foundation, a solid foundation, and an installed caisson, and a deep foundation such as a caisson and a pile foundation. In terms of geotechnical engineering, a shallow foundation is equal to or greater than the embedding depth of the foundation width.
[0003]
When selecting the foundation structure, if the supporting ground is shallow, the former shallow foundation is adopted, and if the supporting ground is deep, the foundation is formed by the frictional force of the pile or peripheral surface that is driven so that the tip reaches the supporting layer. A pile, such as a friction pile, is provided in the ground to support the pile, and a pile foundation for supporting the foundation structure is adopted by the pile.
[0004]
[Problems to be solved by the invention]
By the way, in recent years, the foundation structure (main tower foundation) of a long bridge such as a suspension bridge or a cable-stayed bridge is often excavated up to the bedrock serving as a support layer, and a steel caisson transported by sea is laid down. The installation caisson method of casting underwater concrete is adopted.
[0005]
However, in the case where the bedrock layer is deep from the sea bottom, the construction cost will be significantly increased regardless of whether underwater excavation is performed for the caisson to be installed or a separate pile foundation is adopted. On the other hand, since the bedrock of the main tower foundation of the Akashi Kaikyo Bridge spans several tens of meters below the seabed, an installation caisson method using a dip stack as a support layer has been adopted.However, the structure scale was reduced to reduce the ground reaction force. However, there is a problem that a considerable amount of seabed excavation is required to secure the ground strength.
[0006]
Therefore, the main problem of the present invention is to improve the ultimate bearing capacity and strengthen the initial rigidity by reinforcing the ground itself, for example, when installing a substructure using a ground layer having a lower supporting capacity than rock as a supporting layer. It is another object of the present invention to provide a foundation reinforcement structure capable of reducing the size of the structure and the amount of excavation.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, as the present invention according to claim 1, in a ground region below a mounting surface of a substructure and / or a ground region outside the mounting surface, a slip fracture surface of the substructure is penetrated. A foundation reinforcement structure characterized by installing a shear resistor is provided.
[0008]
As a second aspect of the present invention, in the case where a shear resistor is installed in the lower ground area below the installation surface of the substructure, the width dimension of the substructure is B, and the shear from the end of the substructure is set. when the installation range of the resistor was set to L _1, the reinforcing structure of the foundation of claim 1 wherein installing the shear resistance so as to satisfy the relationship L ₁ /B≧0.45 is provided.
[0009]
As the present invention according to claim 3, in case of installing the shear resistance outside the ground area of the installation surface of the substructure, the width of the substructure and by B, only L ₃ from the end portion of the substructure The shear resistor is installed so as to satisfy a relationship of L ₃ /B≧2.5 when a range from a distant position to an intersection between a slip fracture surface and a ground surface is reinforced. A foundation reinforcement structure according to any of the above is provided.
[0010]
According to a fourth aspect of the present invention, there is provided a reinforcement structure for a foundation, wherein a compaction reinforcing pile for compacting the ground is installed in an adjacent ground area around a substructure.
[0011]
As the present invention according to claim 5, when the width of the substructure and B, and compaction installation range of the reinforcing pile from the edge of the substructure and the L _2, L ₂ /B≧0.6 The reinforcing structure of a foundation according to claim 4, wherein the compaction reinforcing pile is installed so as to satisfy the following relationship.
[0012]
According to a sixth aspect of the present invention, there is provided a reinforcing structure for a foundation according to any one of the first to fifth aspects, wherein heads of the shear resistor or the compaction reinforcing pile are connected to each other.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
[First reinforcement mode]
Engineeringly, regarding the fracture surface when the foundation is installed and loaded on the ground, if the bottom surface of the foundation is smooth, the soil immediately below the foundation is easy to move to the side, and the fracture pattern as shown in FIG. It becomes. On the other hand, when the bottom surface of the foundation is rough, the friction between the foundation and the ground is sufficiently effective, resulting in a fracture pattern as shown in FIG. When considering the plastic balance state in the ground, the area immediately below the foundation is called the active area, and is in an elastic balance state. The tendency of the active region to expand in the lateral direction due to the load from the foundation is restrained by the frictional force and the adhesion between the soil and the bottom surface of the foundation. Thus, this active zone behaves as if it were part of the foundation. The adjacent plastic transition region consists of radiation emanating from the base end and a logarithmic spiral centered on it, and the passive region is a resistive region, also called the passive Rankine band.
[0015]
In the following description, the former example in which the base bottom surface is smooth will be described in detail.
As shown in FIG. 2, when the substructure 1 is to be installed on the ground upper surface, in the present invention, in the lower ground region of the installation surface of the substructure 1 and / or in the outer ground region of the installation surface. By installing the shear resistance piles 2, 2,... So as to penetrate the slip fracture surface of the substructure 1, a high reinforcing effect can be obtained with respect to the ultimate supporting force, and similarly high reinforcing can be performed with respect to the initial rigidity. The effect is obtained. Therefore, the pile according to the present invention does not function as a support pile for supporting a substructure, but is installed to increase the shear resistance of the ground.
[0016]
Hereinafter, it will be described more in detail installation mode of the specific shear resistance piles 2, reinforcement to the main働域just below substructure 1, over a range of L ₁ toward the center side from the end portion of the substructure 1, Shear resistance piles 2, 2, ... are installed. The installation range _{L 1} is, when the width of the substructure and _B, L 1 /B≧0.45, preferably, it is desirable to satisfy the relation of _L 1 /B≧0.5. As long as the shear resistance pile penetrating the slip fracture surface is installed, the reinforcing effect can be expected as compared with the case of no reinforcement, but when L ₁ /B≧0.45, as shown in the examples described later, The reinforcement effect is significantly higher.
[0017]
Further separation ground region of the substructure 1, i.e. reinforcement for Passive zone, the shear resistance from the position apart L ₃ from the end portion of the substructure at the intersection before or its neighborhood area S of the sliding fracture surface and ground plane Install the piles 2, 2, .... Distance _{L 3} from the substructure 1, when the width of the substructure 1 and _B, L 3 /B≧2.5, preferably satisfy the relationship of _L 3 /B≧3.0 desirable. As long as the shear resistance pile penetrating the slip fracture surface is installed, the reinforcing effect can be expected as compared with the case of no reinforcement, but when L ₃ /B≧2.5, as shown in the examples described later, The reinforcement effect is significantly higher.
[0018]
As the shear resistance pile 2, all piles having shear resistance can be targeted. Specifically, a pile body such as a steel pipe pile, a hollow steel pipe pile, a concrete cast-in-place pile, and a precast concrete pile can be used. Among these piles, a steel pipe pile is most preferable from the viewpoint of construction. Although the pile length is fixed in the illustrated example, the pile length may be changed for each location or for each group. It is desirable that all the piles of the shear resistance piles 2, 2 ... installed penetrate the shear fracture surface, but the shear fracture surface assumed in the analysis is often different from the actual one. Considering this, it is desirable to set up in a range that allows for some margin.
[0019]
As shown in FIG. 3, the shear resistance pile 2 is constructed by using a template frame 6 in which steel rings 4, 4,... Are interconnected by connecting members 5, 5,. After the shear resistance piles 2, 2,... Are arranged in an arbitrary arrangement, the steel ring 4 and the head of the shear resistance pile 2 are connected to each other so that the entire shear resistance piles 2, 2,. It is desirable to do.
[0020]
In the case of the reinforcement according to the first aspect, the effect of reinforcing the ground can be expected if there is a shear resistor penetrating the slip fracture surface. Therefore, in place of the shear resistance pile, an underground structure such as an underground continuous wall is used. Can be a shear resistor.
[0021]
[Second reinforcement mode]
Next, a second ground reinforcement structure according to the present invention will be described in detail with reference to FIG.
[0022]
Since the shear fracture surface is deep around the substructure 1, when the shear resistance pile 2 is provided so as to penetrate the shear fracture surface, the pile length becomes long and uneconomical. Therefore, in the adjacent ground area around the substructure 1, it is preferable to install the compaction reinforcing piles 3, 3... For the purpose of compacting the ground and improving the ground.
[0023]
Reinforcement of the adjacent ground regions of the substructure 1, over a range of L ₂ from the end of the basic structure 1 towards the outside, so as to install the compaction reinforcing piles 3,3 .... The installation range _{L 2} is, when the width of the substructure 1 and _B, L 2 /B≧0.6, preferably, it is desirable to satisfy the relationship of _L 2 /B≧0.8. As long as the compaction reinforcing piles 3 are installed, the reinforcing effect can be expected as compared with the case of no reinforcement, but when L ₂ /B≧0.6, as shown in the examples described later, The reinforcement effect is significantly higher. It is desirable that the compaction reinforcing piles 3, 3... Be installed together with the shear resistance piles 2, 2,.
[0024]
As described above, the first reinforcing mode and the second reinforcing mode according to the present invention have been described in detail. However, the present reinforcing structure is not limited to a new foundation structure, but also to the outer ground region of the existing foundation structure. 2. If the compaction reinforcing pile 3 is used, it can be used as reinforcement of an existing foundation structure.
[0025]
【Example】
"experimental method"
In this experiment, a loading test was performed to clarify the bearing capacity characteristics of the ground. In the loading test, Toyoura standard sand packed in an earth tank was compacted with a vibrator to create a model ground. The dimensions of the model ground were 1200 mm x 460 mm x 100 mm assuming a plane strain state. Loading was performed using a loading plate having a smooth bottom surface and a loading width B of 50 mm, with the load increment being 10 kPa, until the ground was broken.
[0026]
In the ground reinforced according to the present invention, in order to examine the reinforcing effect, a sliding fracture surface of the ground was assumed as shown in FIG. The test was performed. The piles were inserted at 5 mm intervals. The classification of the experimental cases will be described below.
[0027]
{Circle around (1)} Case 1: Arrangement of piles for shear resistance to the slip fracture surface generated in the active region. {Circle around (2)} Case 2: Arrangement of piles for resisting the plastic region. The experiments above the arrangement of piles for shear resistance to the surface were performed three times for each case, and the average value was used to examine the effect of ground reinforcement.
[0028]
"Experimental result"
The ultimate supporting force P of the unreinforced ground was 143.7 kPa.
[0029]
In case1, the stakes were arranged as shown in FIG. 5, and further classified into four cases by changing the range width L ₁ of the pile (shear resistance piles 2) An experiment was conducted. FIG. 6 shows the relationship between the ultimate supporting force (P) and the installation range (L ₁ / B) of the pile. Ultimate bearing capacity _P, compared almost the constant value at 150kPa approximately in L 1 _/B=0.2~0.4, sharply increases when _L 1 / B is more than _0.45, L 1 / B = When it becomes 0.5, it is greatly improved to 167.3 kPa. This is because, as shown in FIG. 7, when L ₁ /B=0.5, a large number of piles are installed so as to penetrate the sliding fracture surface generated from the center of the loading plate to the edge of the loading plate, and as shown by arrows. It is thought that it can resist the behavior of the ground, and shows high reinforcement effect.
[0030]
In case2, established the pile (compaction reinforcing piles 3) As shown in FIG. 8, and further divided into three cases by changing the installation range L ₂ of pile experiments were conducted. FIG. 9 shows the relationship between the ultimate bearing capacity (P) and the installation range (L ₂ / B) of the pile. When L ₂ / B exceeds 0.6, the ultimate supporting force P sharply increases, and it is confirmed that when L ₂ /B=1.0, the ultimate supporting force P is improved by 17% compared to the unreinforced ground. This is considered to be because the ground was compacted due to the insertion of a large number of piles, and the ground improvement effect was exhibited.
[0031]
In case3, it established the pile (shear resistance pile 2) as shown in FIG. 10, and further classified into two cases by changing the installation position L ₃ of the pile experiments were conducted. FIG. 11 shows the relationship between the ultimate supporting force (P) and the installation position (L ₃ / B) of the pile. When the installation position of the pile was L ₃ /B=2.0, the ultimate supporting force was 147.8 kPa, which was not so much improved. However, the installation position of the pile exceeded L ₃ /B=2.5, and L _{When 3 /} B = 3.0, the ultimate bearing capacity was 163.7 kPa, which was 14% higher than the unreinforced ground. This is because the pile does not penetrate the slip fracture surface at L ₃ /B=2.0, as shown in FIG. On the other hand, at L ₃ /B=3.0, the piles are installed so as to penetrate the fracture surface. By installing the piles so as to penetrate the slip fracture surface, the shear resistance against the fracture of the ground increases, It was confirmed that a high reinforcing effect was exhibited for the ultimate bearing capacity.
[0032]
13 to 15 show the relationship between the installation range and position of the pile in Case 1 to Case 3 and the initial rigidity. As is clear from the figure, in all the experimental cases, the value of the initial tangent coefficient is larger as the installation range of the pile is wider. This is considered to be because the ground was compacted more and the initial tangent coefficient was improved by increasing the installation range of the pile, that is, the number of inserted piles. When L ₁ /B=0.5 and L ₃ /B=3.0, the initial tangent coefficient was greatly improved. From this, it was confirmed that a high reinforcing effect was also obtained for the initial rigidity by installing the pile so as to penetrate the slip fracture surface.
[0033]
【The invention's effect】
As described in detail above, according to the present invention, a shear resistor is installed so as to penetrate the slip fracture surface of the ground, and / or by installing a large number of reinforcing piles in the ground area around the foundation and compacting the ground. Thus, a high reinforcing effect can be obtained for the ultimate supporting force and the initial rigidity of the substructure.
[Brief description of the drawings]
1 (A) and 1 (B) are diagrams showing ground destruction patterns.
FIG. 2 is an example diagram of ground reinforcement by a shear resistance pile 2.
FIG. 3 is a perspective view of a template frame 6;
FIG. 4 is a diagram showing an example of ground reinforcement by a compaction reinforcing pile 3.
FIG. 5 is a diagram showing an arrangement of piles according to Case 1 of the embodiment.
FIG. 6 is a diagram showing the relationship between the installation range of the pile of Case 1 and the ultimate support force.
FIG. 7 is a diagram showing a relationship between a pile and a slip surface in a main working area.
FIG. 8 is a diagram showing an arrangement of piles according to Case 2 of the embodiment.
FIG. 9 is a diagram showing the relationship between the installation range of piles in Case 2 and the ultimate support force.
FIG. 10 is a view showing an arrangement of piles by Case 3 of the embodiment.
FIG. 11 is a diagram showing the relationship between the installation range of piles in Case 3 and the ultimate support force.
FIG. 12 is a diagram showing a relationship between a pile and a slip surface in a passive area.
FIG. 13 is a diagram showing the relationship between the arrangement of piles and the initial rigidity in Case 1.
FIG. 14 is a diagram showing the relationship between the arrangement of piles and the initial rigidity in Case 2.
FIG. 15 is a diagram showing the relationship between the arrangement of piles and the initial rigidity in Case 3;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Foundation structure, 2 ... Shear resistance pile, 3 ... Compaction reinforcement pile, 4 ... Steel ring, 5 ... Connecting member, 6 ... Template frame

Claims (6)

A reinforcement structure for a foundation, wherein a shear resistor is installed so as to penetrate a slip fracture surface of the substructure in a lower ground region and / or an outer ground region of the installation surface of the substructure. In case of installing the installation surface lower ground region shear resistance of the substructure, the width of the substructure and B, and the range of setting the shear resistance from the ends of the substructure and L ₁ when the reinforcing structure of the foundation of claim 1 wherein installing the shear resistance so as to satisfy the relationship L ₁ /B≧0.45. In case of installing the shear resistance outside the ground area of the installation surface of the substructure, and the width of the substructure is B, slip fracture surface from L ₃ a position spaced from the end of the substructure and the ground The foundation according to any one of claims 1 and 2, wherein the shear resistor is installed so as to satisfy a relationship of L ₃ /B≧2.5 when the area before or near the intersection with the surface is reinforced. Reinforcement structure. A reinforcing structure for a foundation, wherein a compaction reinforcing pile for compacting the ground is installed in an adjacent ground area around the foundation structure. Wherein the width dimension of the substructure B, when the compaction installation range of the reinforcing pile from the edge of the substructure and the L _2, the compaction so as to satisfy the relationship of L ₂ /B≧0.6 The reinforcing structure for a foundation according to claim 4, wherein a reinforcing pile is installed. The reinforcing structure for a foundation according to any one of claims 1 to 5, wherein heads of the shear resistor or the compacted reinforcing pile are connected to each other.

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