U.S. patent application number 12/081176 was filed with the patent office on 2008-10-16 for building foundation structure formed with soil improving body and raft foundation and construction method for soil improvement and raft foundation.
Invention is credited to Kinji Takeuchi, Haruyuki Yamamoto.
Application Number | 20080253845 12/081176 |
Document ID | / |
Family ID | 39853857 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253845 |
Kind Code |
A1 |
Takeuchi; Kinji ; et
al. |
October 16, 2008 |
Building foundation structure formed with soil improving body and
raft foundation and construction method for soil improvement and
raft foundation
Abstract
To provide building foundation structure formed with a soil
improving body and raft foundation that can suppress weight
increase of a soil improving body while achieving suppression of
differential settlement and improvement of bearing capacity of the
whole foundation and that can be applied to medium-rise
buildings.
Inventors: |
Takeuchi; Kinji; (Hiroshima,
JP) ; Yamamoto; Haruyuki; (Hiroshima, JP) |
Correspondence
Address: |
KRATZ, QUINTOS & HANSON, LLP
1420 K Street, N.W., Suite 400
WASHINGTON
DC
20005
US
|
Family ID: |
39853857 |
Appl. No.: |
12/081176 |
Filed: |
April 11, 2008 |
Current U.S.
Class: |
405/233 |
Current CPC
Class: |
E02D 27/44 20130101;
E02D 27/14 20130101 |
Class at
Publication: |
405/233 |
International
Class: |
E02D 7/00 20060101
E02D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2007 |
JP |
2007-105055 |
Jul 10, 2007 |
JP |
2007-180466 |
Claims
1. A building foundation structure, comprising: a shallow-layer
soil improving body that improves the subsurface of soft soil or
soil with possible liquefaction occurrence, which is formed by a
horizontal plate form top improving body, periphery improving
bodies that are suspended from the bottom surface of the top
improving body and form outer frames, and at least one internal
improving body that is suspended from the bottom surface of the top
improving body, at the same time links across the outer frames, and
partitions an area inside the periphery improving bodies into a
plurality of areas; a peristyle-form soil improving body including
a plurality of columnar improving bodies that improve the soil,
which are suspended from the bottom surface of the periphery
improving bodies and the internal improving body or suspended and
provided in a row from the bottom surface of a plate in contact
with bottom surfaces of the periphery improving bodies and internal
improving body or the bottom surface of an intermediate in contact
with the bottom surface of the plate; and a raft foundation cast on
the top improving body of the shallow-layer soil improving
body.
2. The building foundation structure according to claim 1, wherein
the peristyle-form soil improving body comprises columnar improving
bodies disposed immediately beneath columns of a building to be
constructed on the raft foundation and columnar improving bodies
provided in a row immediately beneath underground beams.
3. The building foundation structure according to claim 1, wherein
covered cylindrical cap materials are fitted over to the top end
part of the columnar improving body.
4. A construction method for soil improvement and raft foundation,
comprising the steps of: digging down the subsurface of soft soil
or soil with possible liquefaction occurrence in a form of a
shallow-layer soil improving body of a soil improving body; forming
a peristyle-form soil improving body by agitating while injecting a
solidification material and water after excavating the soil in a
form of columnar improving bodies, or by adding and mixing a
solidification material to soil taken by excavating the soil in the
form of the columnar improving bodies and backfilling, and
compacting after mixing and agitating; forming the shallow-layer
soil improving body by adding and mixing a solidification material
to the soil taken by excavating the soil in the form of the
shallow-layer soil improving body and backfilling and screeding,
and compacting; and building a raft foundation of reinforced
concrete construction on a top improving body of the shallow-layer
soil improving body, wherein the soil improving body comprises: the
shallow-layer soil improving body that is formed by the horizontal
plate form top improving body, periphery improving bodies that are
suspended from the bottom surface of the top improving body and
form outer frames, and at least one internal improving body that is
suspended from the bottom surface of the top improving body, at the
same time links across the outer frames, and partitions an area
inside the periphery improving bodies into a plurality of areas;
and the peristyle-form soil improving body including a plurality of
the columnar improving bodies suspended and provided in a row from
the bottom surfaces of the periphery improving bodies and the
internal improving body.
5. A construction method for soil improvement and raft foundation,
comprising the steps of: digging down the subsurface of soft soil
or soil with possible liquefaction occurrence in a form of a
shallow-layer soil improving body of a soil improving body; forming
a peristyle-form soil improving body by agitating while injecting a
solidification material and water after excavating the soil in a
form of the columnar improving bodies, or by adding and mixing a
solidification material to soil taken by excavating the soil in the
form of the columnar improving bodies and backfilling, and
compacting after mixing and agitating; mounting a plate or an
intermediate as well as the plate on the top end surface of the
peristyle-form soil improving body; forming the shallow-layer soil
improving body by adding and mixing a solidification material to
the soil taken by excavating the soil in the form of the
shallow-layer soil improving body and backfilling and screeding,
and compacting; and building a raft foundation of reinforced
concrete construction on a top improving body of the shallow-layer
soil improving body, wherein the soil improving body comprises: the
shallow-layer soil improving body that is formed by the horizontal
plate form top improving body, periphery improving bodies that are
suspended from the bottom surface of the top improving body and
form outer frames, and at least one internal improving body that is
suspended from the bottom surface of the top improving body, at the
same time links across the outer frames, and partitions an area
inside the periphery improving bodies into a plurality of areas;
and the peristyle-form soil improving body improving a plurality of
the columnar improving bodies that are suspended and provided in a
row from the bottom surface of the plate in contact with the bottom
surfaces of the periphery improving bodies and the internal
improving body or the bottom surface of the intermediate in contact
with the bottom surface of the plate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to building foundation
structure formed with a soil improving body that improves soft soil
or soil in which liquefaction occurrence is foreseen at the time of
earthquakes and raft foundation cast on the soil improving body and
a construction method for soil improvement and raft foundation.
[0003] 2. Description of the Background Art
[0004] As a foundation for a building for soft soil or soil with
possible liquefaction occurrence at the time of earthquakes,
Japanese Unexamined Patent Publication No. 61-5114 (FIG. 1 and FIG.
2) discloses increasing rigidity as the whole soil and preventing
damage to structure by liquefaction of the soil by penetrating into
and drawing out of a soil while rotating an agitation blade of a
deep mixing soil stabilizer, supplying an agglomeration chemical to
discharge to the vicinity of the agitation blade at the time of
penetration, agitating and mixing in the soil and allowing the
agglomeration chemical to solidify, and forming a underground wall
made up of lattice-like or other-shape soil improving bodies
(Patent Document 1). Japanese Unexamined Patent Publication No.
2000-291022 (FIG. 1, FIG. 8 and FIG. 9) discloses reducing a mean
settlement amount and a differential settlement amount of
foundation by piled raft foundation which uses spread foundation in
combination with pile foundation, formed by placing concrete piles
beneath spread foundation such as continuous footing or raft
foundation (Patent Document 2). Japanese Patent No. 3608568 (FIG. 1
and FIG. 2) discloses suppressing differential settlement and
suppressing a lateral flow of unimproved soil at the level of the
lower part of the soil improving body while reducing the weight of
a soil improving body, by the soil improving body formed by
improving the subsurface layer of soft soil, which has a horizontal
plate form top improving body, periphery improving bodies suspended
from the bottom surface of the top improving body and forming outer
frames, and at least one internal improving body that is suspended
from the bottom surface of the top improving body, at the same time
links across the outer frames, and partitions an area inside the
periphery improving bodies into a plurality of areas, as well as
raft foundation cast on the soil improving body (Patent Document
3).
SUMMARY OF THE INVENTION
[0005] In the foundation by the underground wall made up of soil
improving bodies of Patent Document 1, columnar soil improving
bodies need to be continuously produced to form a wall, and
therefore, it takes time to build the soil improving bodies and at
the same time the cost increases.
[0006] In addition, in the piled raft foundation as is the case of
Patent Document 2, a large number of reinforced concrete piles need
to be placed beneath the foundation by the use of large heavy
machinery, and as compared to the case in which the soil beneath
the foundation is improved, the weight increases and at the same
time the cost increases.
[0007] As against these, in the configuration having soil improving
bodies formed by improving soft soil into shallow-layer soil and
raft foundation cast on the soil improving bodies of Patent
Document 3, as compared to the foundations of Patent Documents 1
and 2, the foundation is lightweight and at the same time easy to
construct, and is therefore suited for the foundation structure for
buildings which have comparatively small loads and large building
area.
[0008] However, the foundation structure of buildings having the
soil improving bodies and raft foundation of Patent Document 3 may
be sometimes unable to achieve necessary bearing capacity and
thereby unable to be used for the foundation of, for example,
medium-rise reinforced concrete buildings of 5 to 7 stories. The
foundation structure is susceptible to improvement in order to
provide bearing capacity necessary for medium-rise buildings and
render itself applicable to such buildings.
[0009] What the present invention aims at solving in view of the
foregoing conditions is to provide building foundation structure
formed with soil improving bodies and raft foundation and
construction method for soil improvement and raft foundation that
can suppress weight increase of soil improving bodies while
achieving suppression of differential settlement and improvement of
bearing capacity of the overall foundation, achieve high
comparative economy, and are applicable also to medium-rise
buildings.
[0010] In order to solve the above problems, the present invention
provides building foundation structure formed with soil improving
bodies and raft foundation that includes a shallow-layer soil
improving body that improves the subsurface of soft soil or soil
with possible liquefaction occurrence, which is formed by a
horizontal plate form top improving body, periphery improving
bodies that are suspended from the bottom surface of the top
improving body and form outer frames, and at least one internal
improving body that is suspended from the bottom surface of the top
improving body, at the same time links across the outer frames, and
partitions an area inside the periphery improving bodies into a
plurality of areas, a peristyle-form soil improving body including
a plurality of columnar improving bodies that improve the soil,
which are suspended from the bottom surface of the periphery
improving bodies and the internal improving body or suspended and
provided in a row from the bottom surface of a plate in contact
with the bottom surfaces of the periphery improving bodies and the
internal improving body or the bottom surface of an intermediate in
contact with the bottom surface of the plate, and a raft foundation
cast on the top improving body of the shallow-layer soil improving
body.
[0011] It is preferable that the peristyle-form soil improving body
comprises columnar improving bodies disposed immediately beneath
columns of a building to be constructed on the raft foundation and
columnar improving bodies provided in a row immediately beneath
underground beams.
[0012] Furthermore, it is preferable that covered cylindrical cap
materials are fitted over to the top end of the columnar improving
body.
[0013] In order to solve the above problems, the present invention
provides a construction method for soil improvement and raft
foundation that includes the steps of digging down the subsurface
of soft soil or soil with possible liquefaction occurrence in a
form of a shallow-layer soil improving body of a soil improving
body, forming a peristyle-form soil improving body by agitating
while injecting a solidification material and water after
excavating the soil in the form of the columnar improving bodies,
or by adding and mixing a solidification material to soil taken by
excavating the soil in the form of the columnar improving bodies
and backfilling, and compacting after mixing and agitating, forming
the shallow-layer soil improving body by adding and mixing a
solidification material to the soil taken by excavating the soil in
the form of the shallow-layer soil improving body and backfilling
and screeding, and compacting, and building a raft foundation of
reinforced concrete construction on the top improving body of the
shallow-layer soil improving body, wherein the soil improving body
comprises: the shallow-layer soil improving body that is formed by
the horizontal plate form top improving body, periphery improving
bodies that are suspended from the bottom surface of the top
improving body and form outer frames, and at least one internal
improving body that is suspended from the bottom surface of the top
improving body, at the same time links across the outer frames, and
partitions an area inside the periphery improving bodies into a
plurality of areas; and the peristyle-form soil improving body
including a plurality of the columnar improving bodies suspended
and provided in a row from the bottom surfaces of the periphery
improving bodies and the internal improving body.
[0014] In order to solve the above problems, the present invention
provides a construction method for soil improvement and raft
foundation that includes the steps of digging down the subsurface
of soft soil or soil with possible liquefaction occurrence in a
form of a shallow-layer soil improving body of a soil improving
body, forming a peristyle-form soil improving body by agitating
while injecting a solidification material and water after
excavating the soil in the form of the columnar improving bodies,
or by adding and mixing a solidification material to soil taken by
excavating the soil in the form of the columnar improving bodies
and backfilling, and compacting after mixing and agitating,
mounting a plate or an intermediate as well as the plate on the top
end surface of the peristyle-form soil improving body, forming the
shallow-layer soil improving body by adding and mixing a
solidification material to the soil taken by excavating the soil in
the form of the shallow-layer soil improving body and backfilling
and screeding, and compacting, and building a raft foundation of
reinforced concrete construction on the top improving body of the
shallow-layer soil improving body, wherein the soil improving body
comprises: the shallow-layer soil improving body that is formed by
the horizontal plate form top improving body, periphery improving
bodies that are suspended from the bottom surface of the top
improving body and form outer frames, and at least one internal
improving body that is suspended from the bottom surface of the top
improving body, at the same time links across the outer frames, and
partitions an area inside the periphery improving bodies into a
plurality of areas; and the peristyle-form soil improving body
including a plurality of the columnar improving bodies that are
suspended and provided in a row from the bottom surface of the
plate in contact with the bottom surfaces of the periphery
improving bodies and the internal improving body or the bottom
surface of the intermediate in contact with the bottom surface of
the plate.
[0015] The building foundation structure formed with the soil
improving body and raft foundation of the present invention has: a
shallow-layer soil improving body that improves the subsurface of
soft soil or soil with possible liquefaction occurrence, which is
formed by a horizontal plate form top improving body, periphery
improving bodies that are suspended from the bottom surface of the
top improving body and form outer frames, and at least one internal
improving body that is suspended from the bottom surface of the top
improving body, at the same time links across the outer frames, and
partitions an area inside the periphery improving bodies into a
plurality of areas; a peristyle-form soil improving body including
a plurality of columnar improving bodies that improve the soil,
which are suspended from the bottom surface of the periphery
improving bodies and the internal improving body or suspended and
provided in a row from the bottom surface of a plate in contact
with bottom surfaces of the periphery improving bodies and the
internal improving body or the bottom surface of an intermediate in
contact with the bottom surface of the plate; and a raft foundation
cast on the top improving body of the shallow-layer soil improving
body. Therefore, differential settlement can be suppressed and a
lateral flow of unimproved soil at the level of the soil improving
body lower part can be suppressed, while reducing the weight of the
soil improving body as compared to the case in which overall
foundation bottom part is improved.
[0016] In addition, the building load is supported by the
frictional force (circumferential frictional force) of the side
surface and reaction force (tip reaction force) of the bottom end
surface of columnar soil improving bodies that make up a
peristyle-form soil improving body and large bearing capacity is
able to be obtained. Therefore, the present invention can be used
for foundation of medium-rise buildings.
[0017] Furthermore, locations of the columnar improving bodies, the
pitch between adjacent columnar improving bodies and diameter and
length of the columnar improving bodies can be varied to easily
change the circumferential surface frictional force and tip
reaction force. The present invention can be used for buildings of
various shapes and loads by optimizing the cost while securing
performance by controlling sharing ratio of soil contact reaction
force, circumferential surface frictional force, and tip reaction
force and relative settlement rate.
[0018] In addition, columnar improving bodies that make up a
peristyle-form soil improving body are not allowed to be suspended
from the bottom surface of the top improving body but allowed to be
suspended from the bottom surfaces of comparatively thick periphery
improving bodies and internal improving body. It is therefore
possible to efficiently increase the bearing capacity for buildings
while suppressing an increase of the number of columnar improving
bodies.
[0019] In addition, as compared to the configuration to form an
underground wall made up of lattice-like or other-shape soil
improving bodies, the present invention avoids the need of
continuously forming columnar improving bodies to form a wall and
can shorten the construction period and at the same time can reduce
weight and cost.
[0020] Furthermore, as compared to the piled raft foundation, the
present invention is not of a structure to place a large number of
reinforced concrete piles beneath the foundation by the use of
large heavy machinery. It is therefore possible to reduce the
construction period and at the same time to reduce weight and
cost.
[0021] Furthermore, according to the configuration to arrange plate
material or plate material and intermediate between the periphery
improving bodies as well as the internal improving body and
columnar improving bodies, the top surface of the columnar
improving bodies that make up the peristyle-form soil improving
body and the bottom surfaces of the periphery improving bodies and
the internal improving body that make up the shallow-layer soil
improving body can be easily deviated relatively in the horizontal
direction at the time of earthquakes. It is therefore possible to
reduce the seismic force (horizontal force) transmitted to
buildings constructed on the relevant foundation structure and to
greatly reduce the shakiness. Consequently, earthquake-resistant
performance of the overall structure including the relevant
foundation structure and buildings constructed on the structure can
be still more improved.
[0022] In addition, the peristyle-form soil improving body is
configured with columnar improving bodies disposed immediately
beneath columns of a building to be built on the raft foundation
and columnar improving bodies provided in a row immediately beneath
underground beams. Then, in addition to the above-mentioned
effects, the strength and the rigidity of the overall foundation
are improved and the bearing capacity for the building is further
increased.
[0023] Furthermore, when a covered-cylindrical cap material is
fitted over the top end part of the columnar improving body, in
addition to the above-mentioned effect, the plate material (cover
portion of the cap material) will not come off from the columnar
improving body top end surface by earthquakes, and the seismic
isolation reliability described above can be secured over a long
period of time.
[0024] The construction method for soil improvement and raft
foundation related to the present invention includes steps of
digging down the subsurface of soft soil or soil with possible
liquefaction occurrence in a form of a shallow-layer soil improving
body of a soil improving body, forming a peristyle-form soil
improving body by agitating while injecting a solidification
material and water after excavating the soil in a form of the
columnar improving bodies, or by adding and mixing a solidification
material to soil taken by excavating the soil in the form of the
columnar improving bodies and backfilling, and compacting after
mixing and agitating, forming the shallow-layer soil improving body
by adding and mixing a solidification material to the soil taken by
excavating the soil in the form of the shallow-layer soil improving
body and backfilling and screeding, and compacting, and building a
raft foundation of reinforced concrete construction on a top
improving body of the shallow-layer soil improving body, wherein
the soil improving body comprises: the shallow-layer soil improving
body that is formed by the horizontal plate form top improving
body, periphery improving bodies that are suspended from the bottom
surface of the top improving body and form outer frames, and at
least one internal improving body that is suspended from the bottom
surface of the top improving body, at the same time links across
the outer frames, and partitions an area inside the periphery
improving bodies into a plurality of areas; and the peristyle-form
soil improving body including a plurality of columnar improving
bodies suspended and provided in a row from the bottom surfaces of
the periphery improving bodies and the internal improving body. The
present invention is, therefore, able to suppress differential
settlement and suppress a lateral flow of unimproved soil at the
level of the soil improving body lower part while reducing the
weight of the soil improving body as compared to the case in which
the overall foundation lower part has soil improved.
[0025] In addition, as compared to the configuration to form an
underground wall made up of lattice-like or other-shape soil
improving bodies, the present invention avoids the need of
continuously forming columnar improving bodies to form a wall and
can shorten the construction period and at the same time can reduce
weight and cost.
[0026] Furthermore, as compared to the piled raft foundation, the
present invention is not of a structure to place a large number of
reinforced concrete piles beneath the foundation by the use of
large heavy machinery. It is therefore possible to reduce the
construction period and at the same time to reduce weight and
cost.
[0027] In addition, according to the building foundation structure
formed with soil improving bodies and raft foundation obtained by
the construction method for soil improvement and raft foundation of
the present invention, the building load is supported by the
frictional force of the side surface and reaction force of the
bottom end surface of columnar soil improving bodies that make up a
peristyle-form soil improving body in addition to the soil reaction
force of the shallow-layer soil improving body and large bearing
capacity is able to be obtained. Therefore, the present invention
is able to be used for foundation of medium-rise buildings.
[0028] Furthermore, according to the building foundation structure
formed with soil improving bodies and raft foundation obtained by
the construction method for soil improvement and raft foundation of
the present invention, locations of columnar improving bodies, the
pitch between adjacent columnar improving bodies and diameter and
length of columnar improving bodies can be varied to easily change
the circumferential surface frictional force and tip reaction
force. The present invention is able to be used for buildings of
various shapes and loads by optimizing the cost while securing
performance by controlling sharing ratio of soil contact reaction
force, circumferential surface frictional force, and tip reaction
force and relative settlement rate.
[0029] Still more, according to the building foundation structure
formed with soil improving bodies and raft foundation obtained by
the construction method for soil improvement and raft foundation of
the present invention, columnar improving bodies that make up a
peristyle-form soil improving body are not allowed to be suspended
from the bottom surface of the top improving body but allowed to be
suspended from the bottom surfaces of comparatively thick periphery
improving bodies and internal improving body. It is therefore
possible to efficiently increase the bearing capacity for buildings
while suppressing an increase of the number of columnar improving
bodies.
[0030] The construction method for soil improvement and raft
foundation of the present invention includes steps of digging down
the subsurface of soft soil or soil with possible liquefaction
occurrence in a form of a shallow-layer soil improving body of a
soil improving body, forming a peristyle-form soil improving body
by agitating while injecting a solidification material and water
after excavating the soil in a form of the columnar improving
bodies, or by adding and mixing a solidification material to soil
taken by excavating the soil in the form of the columnar improving
bodies and backfilling, and compacting after mixing and agitating,
mounting a plate or an intermediate as well as the plate on the top
end surface of the peristyle-form soil improving body, forming the
shallow-layer soil improving body by adding and mixing a
solidification material to the soil taken by excavating the soil in
the form of the shallow-layer soil improving body and backfilling
and screeding, and compacting, and building a raft foundation of
reinforced concrete construction on a top improving body of the
shallow-layer soil improving body, wherein the soil improving body
comprises the shallow-layer soil improving body that is formed by
the horizontal plate form top improving body, periphery improving
bodies that are suspended from the bottom surface of the top
improving body and form outer frames, and at least one internal
improving body that is suspended from the bottom surface of the top
improving body, at the same time links across the outer frames, and
partitions an area inside the periphery improving bodies into a
plurality of areas, and the peristyle-form soil improving body
including a plurality of the columnar improving bodies that are
suspended and provided in a row from the bottom surface of the
plate in contact with the bottom surfaces of the periphery
improving bodies and the internal improving body or the bottom
surface of the intermediate in contact with the bottom surface of
the plate. Therefore, in addition to the effects of the
above-mentioned construction method for soil improvement and raft
foundation, in the building foundation structure formed with soil
improving bodies and raft foundation obtained by the construction
method for soil improvement and raft foundation related to the
present invention, plate material or plate material and
intermediate are arranged between the periphery improving bodies as
well as the internal improving body and columnar improving bodies.
Consequently, the top surface of the columnar improving bodies that
make up the peristyle-form soil improving body and the bottom
surfaces of the periphery improving bodies and the internal
improving body that make up the shallow-layer soil improving body
are able to be easily deviated relatively in the horizontal
direction at the time of earthquakes. It is therefore possible to
reduce the seismic force (horizontal force) transmitted to
buildings constructed on the relevant foundation structure and to
greatly reduce the shakiness. Consequently, earthquake-resistant
performance of the overall structure including the relevant
foundation structure and buildings constructed on the structure can
be still more improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic view showing a building foundation
structure formed with soil improving bodies and raft foundation
according to one embodiment of the present invention, FIG. 1(a) is
a plan view and FIG. 1(b) is a cross-sectional view on arrow A-A of
FIG. 1(a);
[0032] FIG. 2 is an enlarged plan view of a principal part;
[0033] FIG. 3 is an enlarged longitudinal sectional view of a
principal part;
[0034] FIG. 4 is an enlarged longitudinal sectional view of a
principal part;
[0035] FIG. 5 is an illustration showing soil reaction force of a
shallow-layer soil improving body as well as frictional force of
the side surface and reaction force of the bottom end surface of
peristyle-form soil improving body; and
[0036] FIG. 6 is a schematic view showing a configuration with
plate material interposed between a columnar improving body and a
periphery improving body as well as an internal improving body, and
FIG. 6(a) is an enlarged longitudinal cross-sectional view of a
principal part and FIG. 6(b) is a fragmentary cross-sectional view
in perspective of a covered cylindrical cap material.
DETAILED DESCRIPTION OF THE INVENTION
[0037] A building foundation structure formed with soil improving
bodies and raft foundation related to the present invention uses
both a shallow-layer soil improving body and peristyle-form soil
improving body which improve soft soil or soil from which
liquefaction occurrence is foreseen, and is formed by placing raft
foundation on the shallow-layer soil improving body. Referring to
drawings, embodiments that put the present invention into effect
will be described. In the following embodiments, the case in which
the soil is soft soil will be discussed as examples.
[0038] FIG. 1 to FIG. 3 are schematic views of building foundation
structure formed with soil improving bodies and raft foundation
related to one embodiment of the present invention. FIG. 1(a) is a
plan view, FIG. 1(b) a cross-sectional view on arrow A-A of FIG.
1(a), FIG. 2 an enlarged plan view of a principal part, and FIG. 3
an enlarged longitudinal sectional view of a principal part.
[0039] As shown in FIG. 1 to FIG. 3, a shallow-layer soil improving
body 1 is formed by a horizontal plate form top improving body 6
that is rectangular in a plan view, periphery improving bodies 7, 7
and 8, 8 that are suspended from the bottom surface of the top
improving body 6 and form rectangular outer frames in a plan view,
and internal improving bodies 9, 9 and 10, 10, that are suspended
from the bottom surface of the top improving body 6, link across
the outer frames, and partition an area inside the periphery
improving bodies enclosed by the outer frames into a plurality of
areas.
[0040] The planar shape of the top improving body and the periphery
improving body may be an outer shape formed by linking a plurality
of rectangles, and the planar shapes of the top improving body and
the periphery improving body need not be same. In addition, the
internal improving body is of a shape combining the periphery
improving body and the internal improving body including the
parallel crosses as viewed two-dimensionally as shown in FIG. 1(a),
and may include two-cell by one-cell or two-cell by two-cell
rectangle as viewed two-dimensionally, and a suitable number is
chosen to partition the area inside the periphery improving body
into a plurality of areas in conformity to the outer shape of the
periphery improving body.
[0041] In addition, a peristyle-form soil improving body 2 is
suspended and provided in a row from the bottom surfaces of the
periphery improving bodies 7, 7 and 8, 8 as well as the internal
improving bodies 9, 9 and 10, 10 of the shallow-layer soil
improving body 1 as shown in FIG. 1 and are formed by a plurality
of columnar improving bodies 11, . . . which are stopped in the
midway of soft soil S (for example, soil with an extremely small N
value over the depth of about 20 m) and are not fixed to the
support layer.
[0042] In FIG. 1(a), pitches Px1, Px2, Px3, Py1, Py2, and Py3
between curbs of shallow-layer soil improving body 1 are installed
in a range, for example, from 5 to 20 meters and pitches Qx and Qy
between adjacent columnar improving bodies 11, 11 are set to, for
example, about 2 to 4 meters.
[0043] In addition, in FIG. 3, the thickness of raft foundation 3
is set to about 0.2 to 0.4 meters, the maximum thickness C1 of top
improving body 6 is set to about 0.6 to 1.2 meters, and the
thickness C2 of periphery improving bodies 7, 7 and 8, 8 as well as
the thickness C3 of internal improving bodies 9, 9 and 10, 10 are
set to about 1 to 2 meters, but the thickness C2 may not be the
same with the thickness C3 and for example, the thickness C2 may be
made thicker than that of C3.
[0044] Furthermore, the width B1 of periphery improving bodies 7, 7
and 8, 8 and the width B2 of internal improving bodies 9, 9 and 10,
10 are set to about 3 to 4 meters, but the width B1 may not be the
same with the width B2 and for example, the width B1 may be made
thicker than the width B2.
[0045] Furthermore, the diameter D of columnar improving bodies 11,
. . . is set to about 0.6 to 1 meter and the length (depth) L is
set to about 5 to 7 meters, but the diameter D and the length L may
be suitably varied in accord with locations. For example, in FIG.
1, it is easy to vary the diameter D and length L of columnar
improving bodies 11, . . . beneath poles 5, . . . and the diameter
D and length L of columnar improving bodies 11, . . . beneath
underground beams 4 (see FIG. 3) as well as the pitches Qx and Qy
between adjacent columnar improving bodies 11, 11 in accord with
locations, and by doing like this, the load sharing ratio and the
relative settlement rate may be controlled to achieve desired
values.
[0046] Next discussion will be made on the construction method for
building the soil improving body having the shallow-layer soil
improving body 1 and peristyle-form soil improving body 2.
[0047] In the shallow-layer soil improving body 1 and the
peristyle-form soil improving body 2 shown in FIG. 1(b) and FIG. 3,
first of all, the subsurface on the downside from the soil level GL
of soft soil S is dug down in a form of the shallow-layer soil
improving body 1 by, for example, spading by backhoe.
[0048] Then, by the use of construction machinery such as small
pile driver, a peristyle-form soil improving body 2 is formed by
agitating while injecting a solidification material such as cement
based solidification material and water after excavating the soft
soil S in the form of the columnar improving bodies 11, . . . . Or
the peristyle-form soil improving body 2 is formed by adding and
mixing a solidification material to soil taken by excavating the
soft soil S in the form of columnar improving bodies 11, . . . and
backfilling, and compacting after mixing and agitating.
[0049] Then, the shallow-layer soil improving body 1 is formed by
adding and mixing a solidification material to the soil taken by
excavating the soil in the form of the shallow-layer soil improving
body 1 and backfilling and screeding, and compacting by heavy
machinery, rollers, etc.
[0050] The soil improving body constructed in this way is able to
be applied even when the soft soil layer S is extremely deep and
does not give rise to the lift-up of buildings because the soil
improving body is drawn down together with surrounding soil
subsidence.
[0051] Furthermore, on the top soil improving body 6 of the
shallow-layer soil improving body 1, the raft foundation 3 of
reinforced concrete construction is built. In the raft foundation
3, underground beams 4 of reinforced concrete construction having
the shape two-dimensionally same as that of periphery improving
bodies 7, 7 and 8, 8 and internal improving bodies 9, 9 and 10, 10
of the shallow-layer soil improving body 1 are formed integral with
the raft foundation 3. Furthermore, columns 5, . . . are disposed
upright at the predetermined location of the underground beams
4.
[0052] The raft foundation 3, underground beams 4 and columns 5, .
. . are built on the top soil improving body 6 by setting base
plates, anchor bolts, etc. of the columns 5, . . . , placing
reinforcing bars in the raft foundation 3 and underground beams 4,
casting concrete for the raft foundation 3 and underground beams 4,
and then, building columns 5, . . . . By this kind of
configuration, even when non-uniform load of structure above the
foundation is exerted to the raft foundation 3, the shallow-layer
soil improving body 1 and the raft foundation 3 move in concert and
the load is distributed to achieve nearly uniform load to the soft
soil layer directly beneath, which is the principal cause of
settlement, and differential settlement can be thereby
suppressed.
[0053] FIG. 4 is a longitudinal sectional view showing an example
in which an engaging protrusion 3a to the shallow-layer soil
improving body 1 is installed to the bottom surface of the raft
foundation 3. The engaging protrusion 3a is formed continuously or
intermittently on the bottom surface of the raft foundation 3 at
locations corresponding to periphery improving bodies 7,7 and 8, 8
and internal improving bodies 9, 9 and 10, 10 of the soil improving
body 1. In addition, on the top surface of the shallow-layer soil
improving body 1, engaging depressions (7a, 8a, 9a, and 10a, and
engaging depressions 8a and 10a are shown in FIG. 4) that engage
the engaging protrusion 3a are formed. These engaging depressions
can be formed by assembling formwork at places where the engaging
depressions (8a, 10a, etc.) are formed when the shallow-layer soil
improving body 1 is formed. By the way, the reason why engaging
depressions are formed at the top part of the periphery improving
bodies 7, 7 and 8, 8 as well as the internal improving bodies 9, 9
and 10, 10 of the shallow-layer soil improving body 1 is to prevent
lowering of rigidity and strength of the shallow-layer soil
improving body 1 when portions with reduced thickness may be formed
in the shallow-layer soil improving body 1. Engaging the engaging
protrusion 3a on the bottom surface of the raft foundation 3 with
the engaging depression on the top surface of the shallow-layer
soil improving body 1 can increase unity of the raft foundation 3
with the shallow-layer soil improving body 1 as well as rigidity
and strength of the overall foundation. Consequently, the
differential settlement suppression effect can be still more
increased.
[0054] According to the building foundation structure formed with
the foregoing shallow-layer soil improving body 1, the
peristyle-form soil improving body 2, and raft foundation 3, as
compared to the case of improving the soil for the overall
foundation bottom, differential settlement and a lateral flow of
unimproved soil at the level of the lower part of the soil
improving body can be suppressed while reducing the weight of the
soil improving body.
[0055] In addition, because the weight of the building is supported
by the frictional force (circumferential frictional force) F2, . .
. of the side surface (circumferential surface) of the columnar
improving bodies 11, . . . that make up the peristyle-form soil
improving body 2 and the reaction force (tip reaction force) F3, .
. . of the bottom end surface, in addition to the soil reaction
force (contact soil reaction force) F1 of the shallow-layer soil
improving body 1 shown in FIG. 5, large bearing capacity can be
obtained and increased foundation soil bearing capacity and
suppressed settlement can be achieved. The building foundation
structure can be used as the foundation for medium-rise buildings
(reinforced concrete structure).
[0056] Furthermore, as described above, by varying the locations of
columnar improving bodies 11, . . . , the pitches Qx and Qy between
adjacent columnar improving bodies 11 and 11, as well as the
diameter D and length L of columnar improving bodies 11, . . . ,
the circumferential frictional force F2 and the tip reaction force
F3 can be easily varied. It is therefore possible to use the
building foundation structure formed with the shallow-layer soil
improving body 1, peristyle-form soil improving body 2, and raft
foundation 3 according to the present invention can be used for
buildings of various shapes and loads with the cost optimized while
securing the performance by controlling the bearing ratio of
contact reaction force F1, circumferential frictional force F2, and
tip reaction force F3 and the relative settlement rate.
[0057] Furthermore, because columnar improving bodies 11, . . .
that make up the peristyle-form soil improving body 2 are not
allowed to be suspended from the bottom surface of the top
improving body 6 but allowed to be suspended from bottom surfaces
of comparatively thick periphery improving bodies 7, 7 and 8, 8 and
internal improving bodies 9, 9 and 10, 10, it is possible to
efficiently increase the bearing capacity for buildings while
suppressing an increase of the number of columnar improving bodies
11. In particular, configuring the peristyle-form soil improving
body 2 with columnar improving bodies 11, . . . disposed beneath
columns 5, . . . of a building to be constructed on the raft
foundation 3 and columnar improving bodies 11, . . . provided in a
row beneath underground beams 4 can further improve the strength
and the rigidity of the overall foundation and can still more
increase the bearing capacity.
[0058] Furthermore, in the case that the building foundation
structure formed with the shallow-layer soil improving body 1,
peristyle-form soil improving body 2, and raft foundation 3 is used
for the soil in which liquefaction occurrence is foreseen, the soil
under the building is partitioned and bound by the peristyle-form
soil improving body 2 and is therefore stabilized, and the
liquefaction resistance can be markedly increased.
[0059] Furthermore, even in the case of the soil in which
consolidation lowering is foreseen, installing the peristyle-form
soil improving body 2 can suppress differential settlement still
more efficiently than in the case of the shallow-layer soil
improving body 1 only.
[0060] In addition, as compared to the configuration to form an
underground wall made up of lattice-like or other-shape soil
improving bodies, the present invention avoids the need of
continuously forming columnar improving bodies to form a wall and
can therefore shorten the construction period and at the same time
can reduce weight and cost.
[0061] Furthermore, as compared to the piled raft foundation, the
present invention is not of a structure to place a large number of
reinforced concrete piles beneath the foundation by the use of
large heavy machinery. It is therefore possible to reduce the
construction period and at the same time to reduce weight and
cost.
[0062] FIG. 6 shows a configuration with plate materials interposed
between columnar improving bodies 11, . . . and periphery improving
bodies 7, 7 and 8, 8 as well as internal improving bodies 9, 9 and
10, 10 so that the top end surfaces of the columnar improving
bodies 11, . . . do not come directly in contact with the bottom
surfaces of the periphery improving bodies 7, 7 and 8, 8 and the
internal improving bodies 9, 9 and 10, 10, unlike the configuration
in which the columnar improving bodies 11, . . . are suspended from
the bottom surfaces of periphery improving bodies 7, 7 and 8, 8 and
internal improving bodies 9, 9 and 10, 10 as shown in FIG. 1(b),
FIG. 3 and FIG. 4. FIG. 6(a) is an enlarged longitudinal
cross-sectional view of a principal part and FIG. 6(b) is a
fragmentary cross-sectional view in perspective of a covered
cylindrical cap material 12 including the plate material.
[0063] That is, in the configuration shown in FIG. 6, after forming
each of the columnar improving bodies 11, . . . which make up the
peristyle-form soil improving body 2, on the top end part of these
columnar improving bodies 11, . . . , covered cylindrical cap
materials 12, . . . are fitted over, and on these cap material 12,
. . . , a shallow-layer soil improving body 1 is constructed.
[0064] Consequently, the columnar improving bodies 11, . . . are
suspended from the bottom surface of the plate material (disk-form
cover 12A of cap material 12), which comes in contact with the
bottom surfaces of the periphery improving bodies 7, 7 and 8, 8 and
the internal improving bodies 9, 9 and 10, 10.
[0065] The cap material 12 is composed with a disk-shape cover 12A
which is plate material interposed between columnar improving
bodies 11, . . . and periphery improving bodies 7, 7 and 8, 8 as
well as internal improving bodies 9, 9 and 10, 10 and annular
cylinder 12B attached to the side surface of columnar improving
bodies 11, . . . , with the top end surface of each of columnar
improving bodies 11, . . . , the bottom surface 12a of the cover
12A comes in contact, and with the top end side surface of each of
the columnar improving bodies 11, . . . , the inner side surface
12b of the cylinder 12B comes in contact. The cap material 12, . .
. may be freely fitted to the top end part of columnar improving
bodies 11, . . . in such a manner that a clearance is provided
between the top end side surface of columnar improving bodies 11, .
. . and the inner side surface of 12b of the cylinder 12B.
[0066] In addition, on the bottom side of the plate material (for
example, the cover 12A), another plate material or intermediates
such as level mortar may be disposed. For example, on the lower
side of the plate material, a single or a plurality of different
plate material may be disposed, below which level mortar, etc. may
be arranged.
[0067] The plate material is preferably, fluororesin such as
polytetrafuluoroethylene (tetrafluoride), etc. or polyacetal,
polypropylene, polyethylene terephthalate, nylon, or ABS and other
synthetic resin, or stainless steel or aluminum alloys and other
metals, or metals to the surfaces of which fluororesin, etc. are
coated, and it is preferable to achieve small frictional
coefficient.
[0068] According to the configuration to arrange plate material
(disk-shape cover 12A of cap material 12) or plate material and
intermediate which comes in contact with the bottom surface of the
plate material between columnar improving bodies 11, . . . and
periphery improving bodies 7, 7 and 8, 8 as well as internal
improving bodies 9, 9 and 10, 10, except the cap material 12, the
configuration is exactly the same as that of FIG. 1 to FIG. 5, and
thus the working-effects by the configuration of FIG. 1 to FIG. 5
are achieved. In addition to the working effects, the top surface
of the columnar improving bodies 11, . . . that make up the
peristyle-form soil improving body 2 and the bottom surfaces of
periphery improving bodies 7, 7 and 8, 8 as well as internal
improving bodies 9, 9 and 10, 10 that make up the shallow-layer
soil improving body 1 can be easily deviated (deviated relatively
in the horizontal direction) at the time of earthquakes. It is
therefore possible to reduce the seismic force (horizontal force)
transmitted to buildings constructed on the relevant foundation
structure and to greatly reduce the shakiness. Consequently,
earthquake-resistant performance of the overall structure including
the building foundation structure and buildings constructed on the
structure as shown in FIG. 6 can be still more improved.
[0069] The example shown in FIG. 6 is the configuration in which
the covered cylindrical cap materials 12, . . . are fitted over the
top end of columnar improving bodies 11, . . . , but the cap
material may not be a covered cylindrical cap material of this kind
but, for example, may be a covered polygonal cylindrical cap
material such as covered rectangular cylindrical shape.
Alternatively, between columnar improving bodies 11, . . . and
periphery improving bodies 7, 7 and 8, 8 and internal improving
bodies 9, 9 and 10, 10, for example, plate materials may be
interposed, and therefore, disk or polygonal plate, or other plate
material alone may be used. However, according to the configuration
in which a covered-cylindrical cap material is fitted over top end
parts of columnar improving bodies 11, . . . , the plate material
(disk-shape cover 12A in the example of FIG. 6) will not come off
from top end surfaces of columnar improving bodies 11, . . . by
earthquakes, and the performance can be continuously exhibited over
a long period of time, and it is therefore a more preferable
embodiment.
[0070] In addition, in the configuration in which another plate
material or intermediates such as level mortar are arranged on the
downside of the plate material, the relative move in the horizontal
direction of the top surface of columnar improving body 11 that
composes the peristyle-form soil improving body 2 with respect to
the bottom surface of periphery improving bodies 7, 7 and 8, 8 and
internal improving bodies 9, 9 and 10, 10 that compose the
shallow-layer soil improving body 1 can be made still more stable
and still more reliable at the time of earthquakes.
* * * * *