JP3627771B2 - Base isolation structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a base-isolated base structure, and more particularly to a base-isolated base structure that reduces shock during earthquakes and prevents damage to piles.
[0002]
[Prior art]
In a pile foundation which is one of the foundations of a structure, the lower part of the structure such as a footing and the pile head are connected via a reinforcing bar. For this reason, when a lateral force acts on the structure due to an earthquake or the like, a horizontal force or a rotational force acts on the head of the pile connected to the structure, and the pile body is damaged by a tensile force or a shearing force due to a bending moment. There is a fear. As a countermeasure, a method of placing gravel between the pile head and the lower part of the structure and laying gravel between them has been proposed by the applicant of this application (Japanese Patent Publication No. 1-44482).
[0003]
According to the proposed method, the pile functions as a load bearing only the vertical load of the structure transmitted through the gravel layer. That is, even if a lateral force acts on the structure due to an earthquake or the like, a sliding action occurs between the gravel particles, and a horizontal force and a rotational force are not transmitted to the pile other than the frictional force associated therewith. Therefore, a large tensile stress or shear stress is not generated in the pile.
[0004]
On the other hand, the sliding action of gravel particles has the function of reducing the impact of an earthquake and absorbing and attenuating energy by the frictional force between the gravel particles generated at that time. It may be preferable to improve and quickly converge the gravel interaction.
[0005]
[Problems to be solved by the invention]
The present invention has been made based on the technical background as described above, and achieves the following object.
[0006]
An object of the present invention is to provide a base-isolated foundation structure that reliably transmits a vertical load of a structure to a pile, and does not transmit a horizontal force due to an earthquake to the pile, and has improved buffering action against the impact. It is in.
[0007]
[Means for Solving the Problems]
The present invention employs the following means in order to achieve the above object.
[0008]
That is, according to the present invention, between the head of the pile and the lower part of the structure, there is a granular material having rigidity, and fine particles smaller than the rigid granular material, and fits in a gap formed between the rigid granular materials. The base isolation structure is characterized by interposing a buffer layer made of a mixed granular material mixed with a granular material having a certain degree of elasticity.
[0009]
Moreover, this invention exists in the base isolation structure characterized by the said mixed granular material being accommodated in the several bag body which has a water-permeable function, and these bag bodies are superimposed.
[0010]
Furthermore, the present invention lies in a base-isolated base structure in which a shelf-like body having a water permeability function is laid in a substantially horizontal direction inside the buffer layer.
[0011]
Furthermore, the present invention resides in a base-isolated base structure in which an end of the shelf-like body is fixed to an anchor.
[0012]
In this invention, a structure means what is supported directly or indirectly by piles, such as a building and the footing provided in order to support this as needed.
[0013]
The granular material having rigidity is resistant to compression against the vertical load of the structure and has a function of transmitting the vertical load to the pile. The size is preferably small such as gravel, but is not necessarily uniform. It does not matter if it is not large, and the shape is preferably non-flat, spherical or slightly elliptical. Even if the end is rounded, it is sufficient that the whole is non-flat and round. Specific examples include round gravel, artificial crushed stone, and hard waste plastic particles.
[0014]
The elastic granular material bears a function of expanding and contracting to absorb and attenuate an impact when a lateral force acts on the structure due to an earthquake or the like, and for example, a corrosion-resistant hard rubber is used. It is preferable that the size of the elastic granular material is smaller than that of the rigid granular material, specifically, a size that fits into a gap formed between the rigid granular materials. By doing so, the rigid granular materials are in close contact with each other, and the load of the structure is reliably transmitted to the pile, so that settlement after construction and settlement due to secular deformation due to the elastic granular material do not occur. The laying area of the mixed granular material is larger than the bottom surface of the structure, but the thickness is appropriately set in consideration of the load of the structure.
[0015]
In the ground which is liable to be liquefied, it is preferable to arrange the rigid granular material not only between the structure and the pile but also around the pile. By doing so, the pore water whose pressure has increased during the earthquake is dissipated through the piles and the buffer layer.
[0016]
The bag body is made of a corrosion-resistant and flexible material, and is formed into a bag shape having a strength that cannot be broken by normal handling in a state where the mixed granular material is accommodated. The water permeation function is obtained when the material itself is water permeable, formed in a net shape, or formed with a large number of small holes, etc. In short, it is sufficient that the ground water can easily pass into and out of the bag body.
[0017]
As the shelf-like body, a net-like material, a belt-like material, a sheet-like material, etc. made of a flexible material having a high tensile strength is used, and has a substantially water-permeable function in a state of being stretched in a substantially planar shape. Need to be. The water permeability function is that the material itself is water permeable, the nets and strips are stretched at intervals, and the gaps form water passages, and the strips and sheets have many small holes. In short, it is only necessary that the groundwater can easily pass from one side of the shelf to the other side. Examples of a simple material for the shelf include plastic, woven fabric, and non-woven fabric.
[0018]
As the anchor, a shelf-like body can be stretched, and a rod-like body, a plate-like body or the like made of a material having high rigidity such as a steel material is used.
[0019]
The pile may be either a ready-made pile or a cast-in-place pile.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the present invention. In the case of a pile foundation, the structure 1 including a footing and the like is supported by a pile 3 installed on the ground 2. In this invention, the buffer layer 4 is interposed between the lower part of the structure 1 and the head of the pile 3.
[0021]
The buffer layer 4 is composed of a mixture of a rigid granular material 5 and an elastic granular material 6 such as hard rubber, as shown partially in FIG. Non-flat rounded gravel is used as the rigid granular material 5, and small particles of hard rubber having a size and amount suitable for the gap between the rigid granular materials 5 are used as the elastic granular material 6.
[0022]
In forming the buffer layer 4, first, the pile 3 is constructed by a normal construction method, if it is a ready-made pile, a driving method, an embedding method, or a cast-in-place pile by various cast-in-place pile methods. After the construction of the pile 3, the ground 2 is excavated to a predetermined depth, and the pile head processing of the pile 3 is performed. The rigid granular material 5 and the elastic granular material 6 are mixed in advance, and the mixed granular materials 5 and 6 are laid on the head of the pile 3. At that time, it is compacted by means such as rolling. When the buffer layer 4 is formed, a formwork is placed thereon, the concrete of the structure 1 is placed thereon, the mold is removed after hardening, and the excavated portion is backfilled.
[0023]
According to the foundation structure, the vertical load of the structure 1 is reliably transmitted to the pile 3 via the rigid granular material 5 of the buffer layer 4, so that unequal displacement does not occur. On the other hand, even if a lateral force is applied to the structure 1 due to an earthquake or the like, a sliding action occurs between the mixed granular materials 5 and 6, and a large horizontal force or rotational force is not transmitted to the pile 3. No stress is generated. In addition, at that time, the elastic granular material 6 expands and contracts by receiving a horizontal force and can quickly absorb and attenuate energy. Furthermore, in the ground where liquefaction is likely to occur due to an earthquake, the underground pore water whose pressure has increased is dissipated through the gap between the mixed granular materials 5 and 6 (drain effect), so that the occurrence of the liquefaction phenomenon can be prevented.
[0024]
FIG. 3 is a sectional view showing another embodiment of the present invention. In this embodiment, as shown in FIG. 4, the mixed granular materials 5 and 6 are accommodated in a bag body 7, and the buffer layer 4 is formed by overlapping a large number of the bag bodies 7.
[0025]
The mixed granular materials 5 and 6 are accommodated in an appropriate unit in a loosely movable state in a bag body 7 which is a net bag of corrosion-resistant plastic. The bag body 7 is preferably flat when the mixed granular materials 5 and 6 are accommodated. The bag bodies 7 are sequentially superimposed with the flat direction set as the horizontal direction, but the upper bag body 7 may be disposed between the adjacent lower bag bodies 7 and 7. By doing so, the entire buffer layer 4 can be made dense.
[0026]
According to this embodiment, the mixed granular materials 5 and 6 are restrained by the bag body 7, and it is possible to prevent deformation such as separation of the buffer layer 4 and generation of cavities due to various factors such as ground fluctuation over a long period of time. Moreover, the bag body 7 functions as a reinforcing material for increasing the shear fracture strength in the buffer layer 4, and can prevent the structure 1 from being unevenly settled. Furthermore, since the bag body 7 has a water permeability function, it does not hinder the escape of pore water in the liquefied ground.
[0027]
FIG. 5 is a sectional view showing still another embodiment of the present invention. In this embodiment, a shelf-like body 8 is arranged inside the buffer layer 4. As the shelf-like body 8, for example, a plastic net or grid having corrosion resistance and high tensile strength is used. Such nets or grids are known as geotextiles in the embankment reinforcement earth method.
[0028]
In the case of using a strip-like material, for example, a plastic belt-like material in which a polyethylene outer peripheral material is provided around a polyester core material as the shelf-like body 8, an appropriate number of pieces are laid in the horizontal direction at appropriate intervals in order to ensure a water-permeable function. . When the shelf-like body 8 made of such a belt-like object is installed in a plurality of stages, it is preferable that each stage is stretched in a direction different by 90 degrees in the horizontal direction. The number of steps and the interval of the shelf-like bodies 8 are determined according to the situation of the structure 1, the pile 3, and the like. In some cases, there may be only one shelf 8.
[0029]
Since the buffer layer 4 is partitioned by the shelf-like body 8, the situation of the buffer layer 4 fluctuates from the initial setting state due to various vibrations, weak earthquakes, groundwater, etc. for many years, or locally. The formation of cavities and the like is prevented.
[0030]
Further, when the buffer layer 4 is formed, anchors 9 and 9 made of steel rods are driven at both sides of the width direction or the entire circumference at a required interval. And the shelf-like body 8 is laid between the opposing anchors 9 and 9, and both ends thereof are fixed to the anchors 9 and 9 by appropriate means. The shelf-like body 8 is laid in order from the lower stage alternately with the mixed granular materials 5 and 6.
[0031]
The manner in which the shelf-like body 8 is fixed to the anchor 9 is not particularly limited, and may be appropriate depending on the material, form, etc. of the shelf-like body 8, and is fixed when a tensile stress acts on the shelf-like body 8. It is sufficient that the shelf-like body 8 is firmly fixed without being displaced at the portion.
[0032]
According to this embodiment, the effect of the mixed granular materials 5 and 6 being restrained by the shelf-like body 8 is further improved, and deformation of the buffer layer 4 can be prevented. In addition, the shelf-like body 8 functions as a reinforcing material that increases the shear fracture strength in the buffer layer 4, and there is no risk of uneven settlement of the structure 1, and the load of the structure 1 is also distributed to the surrounding ground. The bearing capacity is larger than that of the pile only. Furthermore, since the shelf-like body 8 has a water permeability function, it does not hinder the escape of pore water in the liquefied ground.
[0033]
【The invention's effect】
As described above, according to the present invention, the vertical load of the structure is reliably transmitted to the pile via the buffer layer, but even if a lateral force acts on the structure due to an earthquake or the like, the vertical load of the structure slips between the mixed granular materials. Since the action occurs and no large horizontal force or rotational force is transmitted to the pile, no large tensile stress or shear stress is generated. Moreover, at that time, the elastic granular material expands and contracts by receiving a horizontal force, and can absorb and attenuate energy quickly.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view illustrating a part of the buffer layer.
FIG. 3 is a cross-sectional view showing another embodiment.
FIG. 4 is an enlarged cross-sectional view of a bag body.
FIG. 5 is a cross-sectional view showing still another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Structure 2 ... Ground 3 ... Pile 4 ... Buffer layer 5 ... Rigid granular material 6 ... Elastic granular material 7 ... Bag body 8 ... Shelf 9 ... Anchor

Claims (4)

Between the head of the pile and the lower part of the structure, there is a granular material having rigidity, and fine particles smaller than the rigid granular material, which are large enough to fit in a gap formed between the rigid granular materials . A base-isolated foundation structure comprising a buffer layer made of a mixed granular material mixed with an elastic granular material. The base isolation structure according to claim 1, wherein the mixed granular material is accommodated in a plurality of bags having a water permeability function, and these bags are superimposed. The base-isolated foundation structure according to claim 1, wherein a shelf-like body having a water permeability function is laid in a substantially horizontal direction inside the buffer layer. The base-isolated foundation structure according to claim 3, wherein an end of the shelf-like body is fixed to an anchor.

Images