JPH09177094A - Base isolating foundation structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the cushioning effect on an impact to a pile by interposing a cushioning layer formed of a mixture of a rigid granular material and an elastic granular material between the head part of the pile and a structure lower part. SOLUTION: A cushioning layer 4 is interposed between the lower part of a structure 1 and the head part of a pile 3. The cushioning layer 4 is formed of a mixture of a rigid granular material 5 and an elastic granular material 6 such as hard rubber. As the rigid granular material 5, non-flat round gravel is used, and as the elastic granular material 6, a small particle of hard rubber having a size and quantity suitable to the void of the rigid granular material 5 is used. Even when a horizontal force acts on the structure 1 by an earthquake, a sliding action is caused between the mixed granular materials 5, 6, and no large horizontal force or rotating force is transmitted to the pile 3. Further, the elastic granular material 6 is extended and contracted by receiving the horizontal force at that time, so that the energy can be quickly absorbed and damped, and the underground pore water is scattered through the void of the mixed granular materials 5, 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base-isolated base structure, and more particularly, to a base-isolated base structure that absorbs shock during an earthquake and prevents damage to piles.

[0002]

2. Description of the Related Art In a pile foundation, which is one of the foundations of structures, it is a normal structure that the lower portion of the structure such as footing and the pile head are connected via a reinforcing bar. Therefore, when a lateral force is applied to the structure due to an earthquake or the like, horizontal and rotational forces act on the heads of the piles connected to the structure, and the pile body is damaged by the tensile force and shearing force due to the bending moment. There is a fear. As a countermeasure, a method of laying gravel between the pile head and the lower part of the structure in a non-connected state has been conventionally proposed by the applicant of this application (Japanese Patent Publication No. 1-448).
No. 52).

According to this proposed method, the pile functions only to bear 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 the horizontal force and the rotational force are not transmitted to the pile other than the frictional force associated therewith. Therefore, no large tensile stress or shear stress is generated in the pile.

On the other hand, the sliding action of the gravel particles has a function of alleviating the impact of the earthquake and absorbing and attenuating energy by the frictional force between the gravel particles generated at that time, but depending on the condition of the ground, etc. It may be preferable to further improve the action and quickly converge the mutual movement of the gravel.

[0005]

SUMMARY OF THE INVENTION The present invention has been made on the basis of the above technical background, and has the following objects.

An object of the present invention is to provide a base-isolated base structure which 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 which has an improved cushioning action against the impact. To provide.

[0007]

The present invention employs the following means in order to achieve the above object.

That is, the present invention is characterized in that a buffer layer made of a mixed granular material in which a granular material having rigidity and a granular material having elasticity are mixed is interposed between the head portion of the pile and the lower portion of the structure. It is in the seismic isolation basic structure.

Further, the present invention is a seismic isolation basic structure characterized in that the mixed granular material is housed in a plurality of bags having a water permeable function, and these bags are superposed.

Further, the present invention is the seismic isolation basic structure, characterized in that a shelf-like body having a water permeable function is laid in a substantially horizontal direction inside the buffer layer.

Furthermore, the present invention is the base isolation structure, characterized in that the ends of the shelves are fixed to anchors.

In the present invention, a structure is a building,
It refers to those that are directly or indirectly supported by piles, such as footings that are provided to support this as needed.

The granular material having rigidity has a compression resistance against the vertical load of the structure and has a function of transmitting the vertical load to the pile, and the size thereof is preferably as small as gravel. The shape is not necessarily uniform, and the shape is preferably non-flat, spherical or slightly ellipsoidal. Even if the ends are square, it is sufficient if the whole is flat and round. Specific examples include rounded gravel, artificial crushed stone, and hard waste plastic particles.

The elastic granular material has a function of expanding and contracting when a lateral force is applied to the structure due to an earthquake or the like to absorb and damp the impact. For example, a corrosion-resistant hard rubber is used. It is preferable that the elastic granular material has a size smaller than that of the rigid granular material, specifically, a size that can be accommodated in a gap formed between the rigid granular materials. By doing so, the rigid granular materials are in close contact with each other to reliably transfer the load of the structure to the pile, and the settlement due to the elastic granular material after construction and the settlement due to aged deformation do not occur. The laid area of the mixed granular material is made larger than the bottom surface of the structure, but the thickness thereof is appropriately set in consideration of the load of the structure and the like.

In the ground which is likely to be liquefied, it is preferable to dispose the rigid granular material not only between the structure and the pile but also around the pile. By doing so, the pore water that increased in pressure during the earthquake will be dissipated around the pile and through the buffer layer.

As the bag body, a bag made of a flexible material having corrosion resistance is used, and is formed into a bag shape having a strength that does not break by ordinary handling while containing the mixed granular material. As for the water permeability function, the material itself is water permeable,
It may be obtained by a mesh-like material, a material having a large number of small holes, or the like, that is, groundwater can easily pass through the inside and outside of the bag.

As the shelf-like body, a net-like material, a belt-like material, a sheet-like material or the like made of a material which is flexible and has a high tensile strength is used, and it is substantially water-permeable when it is stretched in a substantially planar shape. Must have functionality. As for the water permeation function, the material itself is water permeable, the nets and strips are stretched at intervals, and the gaps form water permeable passages, and the strips and sheets have many small holes. Etc., that is, the groundwater can easily pass from one side of the shelf to the other side. As a simple material for the shelf, plastic, woven fabric, non-woven fabric and the like can be mentioned.

As the anchor, a rack-shaped body can be stretched around the anchor, and a rod-shaped body, a plate-shaped body or the like made of a material having high rigidity such as a steel material is used.

The pile may be a ready-made pile or a cast-in-place pile.

[0020]

BEST MODE FOR CARRYING OUT 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 footings and the like is supported by piles 3 installed on the ground 2.
In the present invention, the buffer layer 4 is interposed between the lower portion of the structure 1 and the head of the pile 3.

The buffer layer 4, as shown in a partially enlarged view in FIG. 2, has a rigid granular material 5 and an elastic granular material 6 such as hard rubber.
It consists of a mixture of and. The non-flat rounded gravel is used as the rigid granular material 5, and the elastic granular material 6 is a small particle of hard rubber having a size and amount that fits into the gap of the rigid granular material 5.

In forming the buffer layer 4, first, the pile 3 is constructed by a normal construction method, a precast pile driving method, a buried construction method, or a cast-in-place pile method of various cast-in-place pile construction methods. After construction of the pile 3, excavate the ground 2 to a predetermined depth,
Pile head processing of 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 compaction. After the buffer layer 4 is formed, a mold is placed on the buffer layer 4, concrete of the structure 1 is poured, and after hardening, the mold is removed and the excavated portion is backfilled.

According to the above basic structure, the vertical load of the structure 1 is surely transmitted to the pile 3 through 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 acts on the structure 1 due to an earthquake or the like, the mixed granular material 5,
Since a sliding action occurs between 6 and a large horizontal force or a rotational force is not transmitted to the pile 3, a large tensile stress or shear stress does not occur. Moreover, at that time, the elastic granular material 6 receives the horizontal force and expands and contracts, so that the energy can be quickly absorbed and attenuated. Further, in the ground where liquefaction is likely to occur due to an earthquake, the underground pore water whose pressure has increased dissipates through the gap between the mixed granular materials 5 and 6 (drain effect), so that the liquefaction phenomenon can be prevented.

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 a large number of the bag bodies 7 are superposed to form a buffer layer 4.

The mixed granular materials 5 and 6 are accommodated in appropriate units in a loose state in a movable state in a bag body 7 which is a mesh bag of corrosion-resistant plastic. The bag body 7 is preferably flat as a whole when the mixed granular materials 5 and 6 are stored. The bags 7 are sequentially overlapped with the flat direction being the horizontal direction, but the upper bag 7 is adjacent to the lower adjacent bag 7,
It is good to arrange it between seven. By doing so, the entire buffer layer 4 can be made dense.

According to this embodiment, the mixed granular material 5,
6 is 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. Further, the bag body 7 functions as a reinforcing material for increasing the shear fracture strength in the buffer layer 4, and the structure 1
It is possible to prevent uneven settlement. Further, since the bag body 7 has a water permeable function, it does not prevent the escape of pore water in the liquefied ground.

FIG. 5 is a sectional view showing still another embodiment of the present invention. In this embodiment, the shelves 8 are arranged inside the buffer layer 4. As the shelf 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 embankment reinforced soil construction methods and the like.

In the case where a belt-shaped material, for example, a plastic belt-shaped material in which a polyethylene outer peripheral material is provided around a polyester core material is used as the shelf-like body 8, an appropriate number of sheets are provided in the horizontal direction at appropriate intervals to ensure a water permeation function. Is laid.
When a plurality of shelves 8 made of such strips are installed, it is preferable that the shelves 8 are stretched in different directions by 90 degrees in each horizontal direction. The number of steps and the intervals of the shelves 8 are determined according to the situation of the structure 1, the pile 3, and the like. In some cases,
It is possible that the rack 8 has only one stage.

Since the buffer layer 4 is divided by the shelves 8, the condition of the buffer layer 4 may fluctuate from the initially set state due to the influence of various vibrations, weak earthquakes, ground water, and the like in the surroundings for many years. It is possible to prevent the formation of cavities locally.

Further, when forming the buffer layer 4, anchors 9 made of steel rods are driven at required intervals on both sides or the entire circumference in the width direction thereof. And the opposite anchor 9,
The shelf-like body 8 is laid between 9 and both ends thereof are fixed to the anchors 9, 9 by appropriate means. The shelves 8 are mixed granular materials 5, 6
And will be laid alternately from the bottom.

The manner of fixing the shelf-like body 8 to the anchor 9 is not particularly limited and may be any suitable one depending on the material and form of the shelf-like body 8, and when tensile stress acts on the shelf-like body 8. To
It suffices that the shelf-like body 8 is firmly fixed without being displaced at the fixed portion.

According to this embodiment, the mixed granular material 5,
The function and effect of 6 being restrained by the shelves 8 are further improved, and the deformation of the buffer layer 4 can be prevented. Further, the shelf-like body 8 functions as a reinforcing material for increasing the shear fracture strength in the buffer layer 4, eliminating the risk of uneven settlement of the structure 1,
Since the load of the structure 1 is also distributed to the surrounding ground, the supporting force becomes larger than that when only the pile is used. Further, since the ledge 8 has a water permeable function, it does not prevent the escape of pore water in the liquefied ground.

[0033]

As described above, according to the present invention, the vertical load of the structure is surely transmitted to the pile through the buffer layer, and even if the lateral force acts on the structure due to an earthquake or the like, the mixture is mixed. Since a sliding action occurs between the granular materials and a large horizontal force or a rotational force is not transmitted to the pile, a large tensile stress or shear stress does not occur. Moreover, at that time, the elastic granular material expands and contracts by receiving a horizontal force, so that energy can be quickly absorbed and attenuated.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing a part of the buffer layer shown in FIG.

FIG. 3 is a sectional view showing another embodiment.

FIG. 4 is an enlarged sectional view showing 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 body 9 ... Anchor

Claims (4)

[Claims] 1. A buffer layer made of a mixed granular material in which a granular material having rigidity and a granular material having elasticity are mixed is interposed between the head portion of the pile and the lower portion of the structure. Earthquake foundation structure. 2. The seismic isolation base structure according to claim 1, wherein the mixed granular material is contained in a plurality of bags having a water permeable function, and these bags are superposed on each other. 3. The seismic isolation foundation structure according to claim 1, wherein a shelf-like body having a water permeable function is laid in a substantially horizontal direction inside the buffer layer. 4. The seismic isolation base structure according to claim 3, wherein an end of the shelf is fixed to an anchor.