JPH1113069A - Settlement preventing foundation structure and foundation work method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the load for unit area, prevent or reduce settlement, and reduce the cost by providing a spread foundation on the upper face center section of a lightweight layer buried in a soil layer, and mounting a structure on the surface portion of the foundation. SOLUTION: A lightweight layer 3 constituted of foam styrol blocks, water granulated slag, or PET bottles and having the density lower than that of a soil layer 5 is arranged at the lower section of a hole excavated in the soil layer 5. When the PET bottles are used, the capped PET bottles are erected in close contact with each other on a plate-like member, and a plate-like member is arranged on them, and concrete is filled as a binder to integrate them. A spread foundation 1 made of reinforced or unreinforced concrete is arranged in contact with the upper face center position of the lightweight layer 3, the foundation 1 and the lightweight layer 3 are back-filled, and a structure 7 is mounted on the surface portion of the foundation 1. Since the total weight of the structure 7 and the foundation 1 is received by the widearea lightweight layer 3, the load for unit area is reduced, settlement can be prevented or reduced, the cost is reduced, and industrial wastes can be effectively utilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foundation structure or a foundation construction method for receiving a load on a building, and more particularly to a foundation structure or a foundation construction method for preventing the foundation from sinking due to a load applied to the foundation.

[0002]

2. Description of the Related Art A structure built on the ground is directly or indirectly supported on the ground via a foundation. Therefore, the foundation should be able to stably support the weight of the structure and various loads applied thereto on the ground so as not to cause obstacles such as unexpected settlement, inclination, movement, deformation, and vibration of the structure. Must be something. The ground must also be able to sustain this load.

[0003] As described above, the foundation structure is formed by the foundation that supports the load due to the weight of the structure and transmits the load to the ground, and the ground that supports the load transmitted from the foundation. Therefore, the foundation structure to be formed is determined in accordance with the state of the ground on which the foundation structure is to be formed and the load to be supported, while obtaining sufficient supporting force and the like and also considering economic efficiency.

[0004] For example, if the soil layer capable of supporting the load is located in a relatively shallow place, a spreading foundation can be employed. There are two types of spread foundations, a solid foundation and a footing foundation, both of which can be generally formed at lower cost than a pile foundation, a pillar foundation, and the like. However, the spreading foundation cannot be adopted unless the support layer is relatively shallow and the load is relatively small, otherwise the foundation may sink over time and cause serious damage. is there.
Therefore, when the upper layer is weak, it is necessary to transmit the load to a deeper and more robust supporting layer by a pile foundation or a pier foundation. The pile foundations and the pier foundations have a problem that the construction work for forming the foundations is large-scale, and the construction cost is high as compared with the spread foundations and the construction period is long.

[0005]

As described above, it is desirable to use a spread foundation in terms of construction cost and construction period, but in the case of the conventional spread foundation, the underlying soil layer cannot withstand the load. The foundation may sink over time.
Conventionally, in such a case, a pile foundation or the like having a problem such as an increase in construction cost has to be adopted. Therefore, the present invention provides a spread foundation capable of avoiding or reducing settlement and increasing the support capacity of the foundation even when the upper soil layer is soft and the support layer is relatively deep and the load is relatively large. Or to provide a method for forming such a spreading foundation.

[0006]

In order to achieve the above-mentioned object, in the foundation structure of the present invention or the construction method thereof, a density lower than that of the soil layer and a sufficient supporting force are provided below the foundation receiving the load. By arranging the light-weight layer, the load on the soil layer below the light-weight layer is reduced, thereby preventing or reducing the settlement of the foundation. That is, the basic structure of the present invention is:
A spreading base structure for preventing or reducing settlement of a foundation under a load, wherein a lightweight layer is provided in a soil layer below a foundation receiving a load of a superstructure, and a density of the lightweight layer is such that Characterized by arranging a lightweight layer that is smaller than the density of the soil layer that existed before providing the lightweight layer,
It is a basic structure. Further, the foundation construction method of the present invention is a foundation construction method for preventing or reducing the settlement of the spread foundation when receiving a load, and in a place where the foundation is formed, the foundation and the lower part of the foundation are provided. Drilling the necessary holes to form the lightweight layer located in the soil layer;
The light-weight layer having a density lower than the density of the soil layer existing before the light-weight layer is provided is reduced by an amount necessary to reduce the load applied to the soil layer existing under the light-weight layer by a predetermined amount. A foundation construction method comprising: burying in a layer and forming the load-bearing foundation above the lightweight layer.

The basis of the present invention refers to a spread foundation including a so-called solid foundation and a footing foundation. As described above, the spread foundation is preferable because the construction cost for forming it is generally lower than that of other types of foundations and the construction period is short. However, in order to adopt the spreading foundation, the support layer must be relatively shallow and the load must be small, otherwise, the settlement over time as a result of the compaction phenomenon becomes a problem, The spreading foundation could not be adopted. The present invention makes it possible to employ a spreading foundation in a place where the occurrence of a certain degree of settlement is conventionally predicted and a spreading foundation could not be adopted, or eliminates a settlement that occurs on the spreading foundation, or It will decrease.

The foundation receives a load from a structure or the like from above and transmits the load to the ground. For this reason,
The foundation must be able to withstand the load and withstand corrosion from the surroundings, and is formed of, for example, reinforced concrete, unreinforced concrete, stone, brick, etc., but is usually formed of reinforced concrete or unreinforced concrete. Is done.

A lightweight layer is located below the foundation under the load of the structure. The foundation and the lightweight layer may be in contact with each other or there may be others between them. The density of the lightweight layer must be less than the density of the soil layer that was present at the location of the lightweight layer prior to providing the lightweight layer. In the present invention, “density” refers to volume density, that is, so-called apparent density. That is, if there is a cavity inside,
It refers to the total mass divided by the total volume including the volume of the cavity. A lightweight layer with a density smaller than the density of the soil layer,
By substituting the soil layer, the load applied to the upper surface of the soil layer existing under the lightweight layer is reduced to prevent or reduce the settlement of the foundation. Also, if the bottom area of the lightweight layer is made larger than the bottom area of the foundation, the area supporting the load becomes larger, so that the load per unit area applied to the upper surface of the soil layer existing under the lightweight layer is also reduced. Can be reduced and the bearing capacity can be increased.

In addition to the aforementioned densities, there are various properties that the lightweight layer must satisfy. For example, since the lightweight layer is buried in the soil for a long time, it must not be corroded by, or react with, soil, moisture, alkali or acid components present in the soil. Further, the lightweight layer must have a sufficient supporting force and must not deform or break even under a long-term load. That is, the lightweight layer needs to be chemically stable in the soil for a long period of time and also physically stable. In addition, it needs to be inexpensive because a certain amount is used.

From the above viewpoints, the materials forming the lightweight layer include polymer materials such as styrene foam, polyethylene, polypropylene and polyethylene terephthalate (PET), inorganic materials such as granulated slag and glass beads, and metals. No. These materials may be formed into a block to form a lightweight layer, but if sufficient strength is obtained, it is also effective to form a cavity inside to reduce the density. Among them, Styrofoam and granulated slag,
It is very preferable because it has chemical stability, physical stability, and economy. In addition, these materials do not need to be new, and industrial wastes and the like can be effectively used, whereby the specific effects of the present invention can be obtained while treating the wastes. For example, a lightweight layer can be formed by a resin bottle (a so-called PET bottle) that is frequently used as a container for selling drinking water.

The PET bottle has a volume of 1 liter, 1.5
Various types such as liter and 2 liter are known, and any of these can be suitably used. The PET layer can be stacked irregularly to form a lightweight layer. However, in order to improve the compressive strength of the lightweight layer in the vertical direction, a plurality of PET bottles are erected (ie, the mouth of the PET bottle is raised or lowered). Toward the PET
The bottle may be fixed (with the longitudinal direction of the bottle facing the vertical direction). In the fixed state, the PET bottles may be tightly bundled so as to touch each other, or an interval may exist between the PET bottles. PET
The mouth of the bottle may be closed or opened by a stopper. However, from the viewpoint of preventing the weight of the lightweight layer formed by the PET bottle from increasing due to the invasion of moisture, earth and sand, etc. into the PET bottle after the foundation structure is installed, the effect of the present invention is reduced, PET
Preferably, the mouth of the bottle is closed. Furthermore, P
If the mouth of the ET bottle is closed, the strength can be increased by the elasticity of the gas (usually air) contained in the PET bottle, which is preferable. When it is necessary to connect and fix the PET bottles to each other, the PET bottles arranged in a desired shape are hardened by a binder such as concrete, or a wire (for example, a resin rope,
The PET bottle can be fixed by tying it to a desired shape by an iron wire or the like. In addition to using the PET bottle in the same shape, it is also possible to use a PET bottle pelletized.

The styrofoam may be block-shaped, granular or powdery.
The block-shaped styrofoam has a density of 0.05 g / c.
m ³ or less, and the effect of reducing the load on the soil layer below the lightweight layer is great. On the other hand, granular or powdery materials can be used by themselves or mixed with an appropriate material, but if the density of the mixture is high, the density of the lightweight layer as a whole increases, Care must be taken because the effect of reducing the load on the lower soil layer is reduced.

The granulated slag can be used by itself or as a mixture with an appropriate one. However, if the density of the mixture is high, the density of the entire lightweight layer increases, and Care must be taken since the effect of reducing the load on the soil layer is reduced.

[0015] In the foundation construction method of the present invention, a hole required for burying and forming a foundation and a lightweight layer disposed thereunder is formed in a soil layer at a place where a foundation structure is to be formed; Embedding the lightweight layer in a predetermined amount and forming a foundation over the lightweight layer. The meaning of the phrase used in the present method is the same as the meaning of the phrase in the above-mentioned basic structure. In addition, the steps of forming a hole, embedding a lightweight layer, and forming a foundation included in the foundation construction method of the present invention do not necessarily need to be performed in this order, and are only necessary, for example, for forming a foundation. It is also possible to embed the lightweight layer after forming the holes, forming the foundation, and then forming the holes necessary for forming the lightweight layer.

The steps of forming a hole, embedding a lightweight layer, and forming a foundation included in the foundation construction method of the present invention may be performed by any known method.

The reduction of the load applied to the soil layer by the foundation structure or the foundation construction method of the present invention can be calculated as follows.
Here, the system used for the calculation is as shown in FIG. 1, and is a columnar structure having a bottom area S [m ² ] buried from the depth (Hh) [m] to H [m] from the soil surface. (Cylinder, elliptical cylinder,
Consider a lightweight layer having the shape of a polygonal column, etc.). The bottom of the foundation is in contact with the upper center of the lightweight layer, and the lightweight layer is pushed vertically downward by the foundation. The force by which the foundation pushes the lightweight layer (that is, the sum of the load applied to the upper part of the foundation from the structure or the like and the mass of the foundation itself) is P [Kg], and the base area of the foundation is A [m ² ]. And the density of the soil layer is D [kg
/ M ³ ], the density of the lightweight layer is d [kg / m ³ ], and the volume of the foundation is ignored in order to simplify the calculation (assuming that the soil layer actually exists in the portion where the foundation actually exists). Calculation), the density of the soil layer is assumed to be the same in all parts.

Consider the pressure that increases with the foundation. The pressure increase in the vertical downward direction, which acts immediately below the central portion of the foundation, is P / A [Kg / m ² ]. On the other hand, when a lightweight layer is provided under the foundation, the pressure increase immediately below the lightweight layer is [dh + P / S-Dh] [Kg / m ² ].
[P / Sh (Dd)] [K
g / m ² ]. Therefore, by providing a lightweight layer, [P (1 / A-1 / S) + h (D-d)] [Kg /
m ² ]. Of these, [P (1
/ A-1 / S)] is the contribution due to the lighter layer bottom area being larger than the foundation bottom area, and [h (D−d)] is due to the lighter layer density being smaller than the soil layer density. The contribution is shown.

Further, when the foundation is formed so that the load per unit area applied to the soil layer existing under the lightweight layer is the same as that applied to the soil layer before the foundation is formed. There is no load increase and no subsidence over time.
In this case, [P / Sh (Dd)] = 0 may be satisfied. For example, P = 50 [ton], S =
10 [m ² ], D = 2000 [Kg / m ³ ], and d = 5
Assuming 0 [Kg / m ³ ], h = 2.56 [m],
By providing a lightweight layer with a base area of 10 [m ² ] and a height of about 2.6 [m] under the foundation, the pressure applied to the soil layer immediately below the lightweight layer while supporting a load of 50 tons is increased at all. And a foundation structure free of settlement problems.

Further, according to the foundation structure and the foundation construction method of the present invention, the load per unit area applied to the soil layer existing under the lightweight layer is larger than that applied to the soil layer before forming the foundation. It can be smaller. In this case,
It suffices to satisfy [P / Sh (D−d)] <0. That is, according to the foundation structure and the foundation construction method of the present invention, since the load per unit area applied to the soil layer existing under the lightweight layer can be freely changed, the subsidence can be performed without selecting a place or soil quality. Problem can be reliably avoided and a foundation with increased bearing capacity can be obtained. The load can also be reduced by making the bottom area of the lightweight layer larger than the bottom area of the foundation.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings based on embodiments, but the present invention is not limited thereto.

In the basic structure of the present invention shown in FIG. 1, the foundation 1 is arranged so as to be in contact with the center of the upper surface of the lightweight layer 3 embedded in the soil layer 5. A structure 7 to be supported by the foundation 1 is mounted on an upper portion of the foundation 1 protruding above the ground surface. Therefore, the load obtained by adding the load of the structure 7 and the weight of the foundation 1 is transmitted from the foundation 1 to the lightweight layer 3.
In this embodiment, the light-weight layer 3 has a rectangular parallelepiped shape, but may have another shape, for example, a polygonal prism such as a quadrangular prism, a pentagonal prism, or a hexagonal prism, a circular cylinder, or an elliptical cylinder. The light-weight layer 3 is formed by combining styrofoam blocks, but may be formed of other materials such as granulated slag. In the case of this embodiment, the lightweight layer 3 and the foundation 1 are in contact with each other, but another material may be interposed between them. The foundation 1 may be any spreading foundation generally used corresponding to the load to be supported, and its structure, material and the like are determined by a known technique.

The load of the structure 7 is 90 tons, and
Is 10 tons, the total load transmitted from the foundation 1 to the lightweight layer 3 is 100 tons. At this time, the bottom area of the lightweight layer 3 is 25 m ² , and the bottom area of the foundation 1 is 5 m ²
And the density of the soil layer is 2000 [Kg / m ³ ], and the density of the lightweight layer 3 formed by styrofoam is 3
0 [Kg / m ³ ]. When only the foundation 1 is arranged and the light-weight layer 3 is not provided thereunder, the pressure increase is 100 tons / 5
m ² = 20,000 [Kg / m ² ]. On the other hand, when the light-weight layer 3 has a thickness of 2 m, the pressure increase [P / S-h]
(D-d)] is 100000 / 25-2 (2000-
30) = 60 [Kg / m ² ], which is almost negligible compared to the case where the lightweight layer 3 is not provided. That is, by providing the lightweight layer 3, the pressure received by the soil layer is almost equal to that before the foundation work is performed. Therefore, in this case, there is almost no possibility of settlement, and a stable basic structure can be obtained.

Next, an embodiment of the foundation work method of the present invention will be described with reference to FIGS. FIG. 2 shows a hole 5a necessary for forming the foundation and the lightweight layer of the present invention.
The figure shows a place excavated in the area. Considering the shape of the foundation and the shape of the lightweight layer, a hole 5a of a required shape
To form The hole 5a is usually formed using a power shovel or the like, but may be formed by any known method for excavating the soil layer. FIG. 3 shows the hole 5 formed in FIG.
2 shows a state in which the light-weight layer 3 is arranged at the lower part of FIG. FIG. 4 shows the foundation 1 formed at the center of the upper surface of the lightweight layer 3 arranged in FIG. The formation of the foundation 1 is usually performed using reinforced concrete, but the method may be performed by any known method.
FIG. 5 shows a state where the foundation 1 shown in FIG. 4 and the lightweight layer 3 located thereunder are backfilled with a soil layer. The upper part of the foundation 1 protrudes above the surface of the soil layer, and a structure is supported on this part to complete the foundation structure as shown in FIG.

FIG. 6 shows a part of a cross section of the lightweight layer of the present invention when the lightweight layer is formed by a PET bottle. A plurality of PET bottles are arranged upright on a plate-like member 12 forming the lower surface of the lightweight layer 3 so as to be in contact with each other. The PET bottles 14 may be arranged so as to be in contact with each other as described above, but may be arranged at an interval depending on the magnitude of the load or the like.
A stopper 14a is provided at the mouth of each PET bottle 14, and the PET bottle 14 is in a sealed state. In this embodiment, the PET bottle is arranged so that the mouth faces upward, but the mouth may be oriented downward. If the mouth faces downward, it is possible to effectively prevent accumulation of water and the like in the PET bottle, which may occur due to breakage of the stopper 14a or the like. A plate member 18 is disposed on the PET bottle 14, and the plate member 12 and the plate member 18 are arranged.
Are arranged so as to be parallel to each other. A space formed between the plate member 12 and the plate member 18,
Space not occupied by PET bottle 14 is concrete 1
Occupied by six. Concrete 16 is made of PE
It is a binder for fixing the T bottle 14, and is used for integrating the plate member 12, the plate member 18, and the PET bottle 14. Although concrete is used in this embodiment, other binders such as an adhesive and mortar can be used. Further, it is not necessary that all of the space formed between the plate-shaped member 12 and the plate-shaped member 18 that is not occupied by the PET bottle is filled with the binder. May be filled only partially.
Since the binder has a large density in many cases, it is preferable to use only a minimum necessary amount in order to reduce the weight of the lightweight layer. For example, the binder may be filled only in the upper and lower parts of the PET bottle 14. Further, instead of using a binder such as concrete, the PET bottle can be fixed by binding using a wire such as resin or metal. The use of such a wire is preferable because it may be possible to reduce the weight as compared with the case of using concrete or the like. This P
The light-weight layer formed by the ET bottle 14, the plate-shaped member 12, the plate-shaped member 18, and the concrete 16 (binder) can also be used by vertically stacking a plurality of layers so as to obtain a desired load reduction effect. .

Since the present invention is configured as described above, it has the following effects.

By arranging the lightweight layer under the load-bearing foundation, the load applied to the soil layer existing under the lightweight layer can be reduced, and the settlement of the foundation can be prevented or reduced.

By using a lightweight layer having a bottom area larger than the bottom area of the foundation, it is possible to reduce the load per unit area applied to the soil layer and increase the bearing capacity of the foundation.

If a lightweight layer is formed by a PET bottle, the cost of raw materials for forming the lightweight layer can be significantly reduced and industrial waste can be effectively used.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing a first step for forming a basic structure according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a second step for forming a basic structure according to one embodiment of the present invention.

FIG. 4 is a sectional view showing a third step for forming a basic structure according to one embodiment of the present invention.

FIG. 5 is a sectional view showing a fourth step for forming a basic structure according to one embodiment of the present invention.

FIG. 6 is a cross-sectional view of a part of the lightweight layer formed by the PET bottle of the present invention.

[Explanation of symbols]

 Reference Signs List 1 foundation 3 lightweight layer 5 soil layer 5a hole 7 structure 12 plate member (lower part) 14 PET bottle 14a stopper 16 concrete (binder) 18 plate member (upper part)

Claims (12)

[Claims] 1. A spread foundation structure for preventing or reducing settlement of a foundation under a load, wherein the lightweight structure is a light layer in a soil layer below a foundation under a load of a superstructure. A spreading base structure, wherein a light-weight layer having a density lower than that of a soil layer existing before providing the light-weight layer is disposed. 2. The method according to claim 1, wherein said foundation is made of reinforced concrete or unreinforced concrete.
The basic structure described in the above. 3. The spreading base structure according to claim 1, wherein the lightweight layer contains styrofoam. 4. The spreading base structure according to claim 1, wherein said lightweight layer contains granulated slag. 5. The spreading base structure according to claim 1, wherein said lightweight layer includes a PET bottle. 6. The load according to claim 1, wherein a load per unit area applied to an upper surface of the soil layer under the lightweight layer is the same as that before the formation of the foundation structure. Expanding base structure. 7. A foundation construction method for preventing or reducing settlement of a spread foundation when receiving a load, wherein the foundation is formed in a place where the foundation is formed and in a soil layer below the foundation. Drilling a hole necessary to form the lightweight layer to be formed, and placing a lightweight layer having a density smaller than the density of the soil layer existing before providing the lightweight layer below the lightweight layer. Burying in the soil layer an amount necessary to reduce the load applied to the existing soil layer by a predetermined amount, and forming a foundation receiving the load above the lightweight layer; . 8. The method according to claim 7, wherein the foundation is formed of reinforced concrete or unreinforced concrete. 9. The method according to claim 7, wherein the lightweight layer contains styrofoam. 10. The foundation construction method according to claim 7, wherein the lightweight layer contains granulated slag. 11. The method according to claim 7, wherein the lightweight layer includes a PET bottle. 12. The load according to claim 7, wherein a load per unit area applied to an upper surface of the soil layer existing under the lightweight layer is the same as that before the foundation work is performed. Foundation construction method.