Note: Descriptions are shown in the official language in which they were submitted.
~34698
This invention relates to pile constructions,
particularly to a method of constructing a cast-in-place
concrete pile with improved end bearing power and s~in
friction.
Cast-in-place concrete pile are generally divided in
two groups: cased piles in which a thin metal casing is
driven into the ground to serve as a form, and uncased
piles where the concrete is placed directly against the
soil. There are several methods of constructing uncased
piles and cased piles. In one method of casting a cased
pile, a core is driven with the casing. After the core is
withdrawn, the casing is filled with concrete. The
casing may be a thin metal shell. In some methods the
shell may be closed at the lower end with a flat or cone-
shaped boot.
Uncased piles may be formed by a temporary casing
which is pulled out after concrete is placed. They may
be also established by drilling holes in the ground and
and casting concrete in the holes.
It is known that cast-in-place concrete piles may be
formed with enlarged bases to reduce the intensity of the
load transferred to the bearing strata. Many methods are
available for such pile constructions. In one method a
shell which is initially partly filled with concrete is
driven by an internal core, the shell is raised and the
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core is forced downward to force the concrete out for
forming an enlarged base. Therea~ter, the casing is
filled with concrete and then pulled out. However, the
methods utili~ed heretofore are found defficient as it is
difficult to achieve a desired extent of enlargement in
base formation. In addition, the conventional cased
piles usually develop reduced skin friction as there are
gaps around the formed piles which are resulted while
driving the shells.
An object of the invention is to provide a method of
constructing a cast-in-place concrete pile with improved
end bearing power and skin friction.
Another object of the invention is to provide a
method which improves the constructions of a cast-in-place
concrete pile to a form with a iarger base formation and
an effective surface area in tight abutment with the
surrounding soil.
The foregoing and other objects can be achieved
in accordance with the invention through the provision of
a method of constructing a cast-in-place concrete pile
which comprises: (a) driving a shell which is closed
temporarily at its lower end with a boots to a certain
depth in the ground; (b) forcing the boot of the shell by
hammering a core -to separate it from the lower end of the
shell and to extend it to a further depth, thereby
causing a hollow between the end of the shell and the
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boot; (c) removing the core from the shell; (d) enlarging
the width of the hollow by soil excavation; and (e)
placing concrete into the enlarged hollow and the shell.
According to the invention, the method may
further includes step (d) preparing a rotary shaft with
collapsible blades and lowering said shaft until it
reaches the hollow. The collapsible blades may be made
of steel chains.
According to the invention, the method m~y further
comprises the steps: placing a central tube passing
through the shell and extending beyond the bottom side of
the enlarged hollow prior to step (e) and forcing a
further charge of concrete through said tube after step
(e) to cause the concrete to penetrate into the soil
surrounding the enlarged base formed and the gap around
the shell.
In one aspect of the invention, the method comprises:
ta) driving a core with a shell into the ground; (b)
removing the core from the shell; (c) placing a central
tube passing through the shell and extending it to the
end of the shell; (d) placing concrete into the shell
through the annular space around the central tube; (e)
allowing the concrete to set; and tf) forcing a further
charge of concrete through the central tube to cause it
to penettate into the soil and the gap surrounding the
shell.
The presently preferred exemplary embodiment will be
described in detail with reference to the following
~23'~698
drawings, wherein:
Fig. 1 illustrates the shell and core which is
placed in the ground;
Fig. 2 illustrates the driving of the boot to
separate it from the shell;
Fig. 3 illustrates a rotary shaft with collapsible
blades placed in the hollow;
Figs. 4 and 5 illustrates the operation of the shaft
for enlargement of the hollow;
Fig. 6 shows a collapsible reinforcement frame
placed in the shell and the hollow;
Fig. 7 illustrates that the shell and the hollow is
provided with a pressurizing tube;
Fig. 8 is a view after the shell and the hollow are
L il led with,concrete;
Fig. 9 is a view after -the soil stabilizing agent is
introduced through the pressurizing tube; and
Fig. 10 is a view after the pile construction is
complete.
"
Referring to Fig. 1, a shell 10 which is in this
embodiment pre~rably a precast concrete pile is provided
with a cone shaped boot 11 at its lower end. The shell 10
is driven into the ground. When it reaches a certain depth,
the cone shaped boot 11 is forced by hammering a core lOa tO
be separated from the lower end oE the shell.
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~lammering is continued until the boot 11 extends into a
Eurther depth of about lm to 2 m, thereby resulting a
hollow 12 between the lower end of the shell and the boot
11, as shown in Fig. 2.
The hollow 12 is further enlarged by soil
excavation. It is requird a rotary shaft with
collapsible blades which can be passed through the shell
10 and then stretched out at beyond the end of the shell.
Preferably, steel chains are used as blades in this
embodiment. A rotary shaft 13 which is incorporated with
steel chains 15 is lowered into the hollow 12 through the
shell 10 and then rotated by a driving means, such as
motor. The lengths of the chains 15 may be chosen
according to how much extent of the base is desired.
The shaft 13 is extended to a depth above the boot as
shown in.Fig. 3.
As the shaft 13 is rotated, the steel chains 15 are
spinning and beating the soil as shown in Fig. 4. For
ef~ective beating of the soil, the shaft may be rotated
in clockwise and counter-clockwise directions
alternatively. Water is jetted into the hollow 12 and
the soil is churned into slurry which is then bailed out
by a known manner. Large size stones and the like which
can not be suspended in the slurry are beaten down by the
chains 15 into the contracted space above the boot 11 as
shown in Fig. 5. As the soil is excavated, the hollow 12
is enlarged. The enlarged hollow 12 may have a size
or radius substantially similar to the length of a steel
` ~3~6~8
chain 15. The volume of the enlarged hollow 12 can be
determined by a supersonic detector.
To keep the rotary shaft 13 in a coaxial
relationship with the shell 10, retaining members 17
which can be made of elastic material,such as rubber are
provided between the rotary shaft 13 and the shell 10.
For reinforcing purpose, a steel frame 14 which is
preferably collapsible is placed in the enlarged hollow
12 and the shell 10 prior to casting concrete, as shown
in Fig. 7.
There is further inserted a pressurizing tube 16
which is extended into the hollow 12 through the shell 10
prior to casting concrete. The tube 16 is advantageously
extended to a region below the enlarged portions of the
hollow 12 which will be filled with concrete as shown in
Figs. 8 and 9, so that the open end of the tube will not
be embedded in the concrete.
A charge of concrete is poured into the hollw 12
through the annular space around the tube 16. To avoid
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the ~ at the end of the tube 16, the tube is
supplied with a flow of water during operation. After
the shell 10 and the enlarged hollow 12 are filled with
concrete as shown in Fig. 8, the concret~ is allowed to
set for 4-5 hours.
Then a soil stabilizing agent is supplied into
the tube 15 and then forced to penetrate into the soil
surrounding the enlarged concrete base 18 as shown in
~23469~
Fig. 9. Subsequent supplying of the soil s-tabilizing
agent causes the agent to rise through the region
surrounding the enlarged base 18 to the region around the
shell 10, thereby improving the soil density and
stability around the shell 10 and the enlarged base 18.
Thereafter, a further charge of concrete is forced
through the tube 16 and penetrated into the soil
surrounding the enlarged base 18, thereby increasing the
size of the base 18 as well as its-skin friction. As the
concrete is supplied through a high pressure, it is then
penetrated into the gap around the shell 10 from the base
as illustrated in Fig. 10. When the concrete sets, an
improved skin friction is developed around the shell 10.
This step is important for improving the skin friction of
the pile. The construction of a pile is complete at this
stage.
It can be appreciated that the method according
to the invention offers an improved pile construction
- with an effective enlarged base which increases the end
bearing power of the pile and with an effective surface
area adhering to the surrounding soil which improves the
skin friction.
With the invention thus explained, it is apparent
that obvious modifications and variations can be made
without departing from the scope of the invention. It
is therefore intended that the invention be limited only
as indicated in the appended claims.
