TECHNICAL FIELD OF THE INVENTION
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The present invention relate to a cast-in-place pile and the
construction process for manufacturing of the cast-in-place
pile.
TECHNICAL BACKGROUND
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In the field of foundation engineering practice, a
construction work where concrete piling is required it is the
conventional practice to drill holes on the ground to the proper
depth with earth auger so the cylindrical cast-in-place concrete
piles can be produced. For friction piles and friction-end-bearing
piles with the frictional force as the main bearing force,
it is necessary to enhance the bearing capacity of a single pile
by lengthening the length of the pile and/or by enlarging the
pile diameter. The length of the pile is determined by the depth
of sustaining layer of the ground. As the pile diameter being
enlarged, the periphery surface will increase in linear relation
with respect to diameter, while the volume will increase in
square relationship accordingly. It is evident that to enlarge
the pile diameter to increase the skin-frictional force of the
pile at the cost of more concrete material would be irrational.
OBJECTIVES OF THE INVENTION
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One of the objectives of the invention is to provide the new
type of cast-in-place piles which will efficiently increase the
bearing capacity of a single pile without increasing materials
to obtain better economic results.
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Another objective of the invention is to provide a new type
of cast-in-place pile group which is formed by the rigid
connection of the cast-in-place piles of the invention with
pre-embedded parts to form the diaphragm wall.
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The third objective of the invention is to provide a
construction process for manufacturing the above mentioned
cast-in-place piles.
SUMMARY OF THE INVENTION
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This invention provides a new type of cast-in-place concrete
pile constructed by grouting concrete into the borehole, the
cross section profile of said borehole being composed of two
or more connected arcs.
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This invention also provides a construction method for the
cast-in-place pile comprising the following process:
- 1)Drilling, to drill a borehole with its cross section
profile composed of more than two connected arcs, to the
designed depth;
- 2)Grouting concrete and lifting auger upward until the
surface of the filling concrete reaches the cave-in
position or above the underground water level;
- 3)Lowing the reinforcing cage;
- 4)Pouring aggregate and supplementary concrete;
- 5)Recharging cement mortar followed by vibro-tamping, and
recharging as required to compensate the shrinkage of the
pile.
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The drilling rig is also a rotary drilling type, but the
borehole has a noncylindrical profile composed of circular
curves . Each section of the curves is circular due to rotary
drilling, however the borehole possesses non-cyclindrical
profile, which is formed by intersection of two or more circular
holes. The following shapes of borehole are ideal ones:
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Borehole of flower shape, which is formed by a central hole
intersected by three or four outer smaller holes;
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Boreholes arranged in a row, which is formed by two or more
circular holes side by side along a straight line and the said
holes are intersected with the neighbor.
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Filled with concrete in above-said holes, the flower-shape-piles
or the row-piles may be formed. The rigid connection
of row-piles with pre-embedded parts will form rowed pile group
into a diaphragm wall.
DESCRIPTION OF THE DRAWINGS
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The description refers to the accompanying drawing in which
like reference characters refer to like parts throughout the
several views and in which:
- FIG. 1 shows schematically the cast-in-place flower-shape-pile;
- FIG. 2 shows schematically cast-in-place row-pile;
- FIG. 3 shows schematically a conventional continuous
underground wall/diaphragm wall;
- FIG. 4 shows schematically the conventional soldier
pile/bulkhead pile;
- FIG. 5 shows schematically the diaphragm wall comprising the
row-piles with rigid connection;
- FIG. 6 shows a plan view in a deep foundation pit supported
by the cast-in-place row-piles connected together;
- FIG. 7 shows a side view of the row-pile support similar to
that in FIG. 6;
- FIG. 8 is the schematic drawing showing the pile formation
process.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
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Referring to the drawings, FIG. 1 and FIG. 2 show the
flower-shape-pile and row-pile respectively. For simplicity,
we adopt the logo S.P. and express their dimensions in the form
as S.P.Dc-nxDs/L, where Dc and Ds represent the diameters ( in
mm) of the central hole and the side/outer holes respectively,
L is the length of the pile ( in m ), n is the number of the
side/outer holes to distinguish the type of the non-cylindrical
cast-in-place piles, for row-pile n = 2; for flower-shape-pile
n = 3 ( basic ) or n = 4 ( optional ).
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With minor modification on the drill rack, the conventional
multi-shaft long auger drilling rig can be used for drilling
non-cylindrical boreholes. For the flower-shape borehole, the
rig has four augers, four shafts, and the central ones are greater
than outers.
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Typical procedure to form cast-in-place concrete pile is
illustrated in FIG. 8, where: 17 shows the drilling process;
18 shows the grouting process after stopping of drilling footage,
23 is grouted concrete/cement, 24 is the belled pier formed by
diffusion under high grouting pressure, like 4 in FIG. 1 as well;
19 shows the process of lowering the reinforcing cage 25 into
the borehole, to lower the cage either by vibrating it or by
loading a drive-in force on it depending on concrete conditions;
20 shows the process of pouring aggregate 26 after the
reinforcing cage being set well, or pouring supplementary
concrete as required; 21 shows the recharging process, cement
mortar passing through the refilling tube 27 to compensate the
shrinkage of the pile; 22 illustrates the vibro-tamping process
with a vibrator 28, and refilling should be repeated.
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For short reinforcing cage , say, about 10 meters concrete
can be pumped into the borehole during the grouting process then
the cage being set by vibration. As the length of cage increasing,
the concrete should be finer to reduce the difficulty to lower
down the cage, the concrete composes fine gravels instead of
coarse aggregate. The longer the cage employed, the finer the
concrete preferred, for cage longer than 20 meters, cement mortar
would be the choice, and aggregate pouring process then followed.
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The industrial application of this invention is possible
because the related equipment and techniques have been proved
to be applicable. Being a new approach in foundation engineering
this invention is suitable for industrial and residential
construction in areas with complicated or special geological
conditions. It has many advantages: rapidity, high efficiency,
good quality, safety and lower cost in operation, and in favor
of the environment protection as well. For instance, the
flower-shape-pile, with the same bearing capacity, can decrease
the material consumption by more than 50%, compared with that
in the cylindrical or rectangular piles. Moreover, when they
are constructed as pile groups, the group-pile effect of the
piles of this invention is lesser than that of the piles with
simple cylindrical profile. Whether it is used as a foundation
pile ( carrying the vertical load, resisting to lifting, or
carrying the alternating load ) or as a diaphragm wall pile,
it would not be inferior to other types. The rigid structure
of well-connected row-piles can be designed as a substitute for
the expensive and time-consuming continuous underground
wall/diaphragm wall with same effectiveness in resisting soil
pressure and barring water. When the row-piles are employed as
a support for deep foundation pit, the construction of temporary
support bodies can be obsolete, it would remarkably save both
materials and working time by combining the piles and wall
together as one integrated structure. The process of hole-boring
and concrete grouting are carrying out consecutively without
intermission, the successive processes as lowering the
reinforcing cage, pouring aggregate, recharging cement followed
up, so the whole procedure would be completed as in one operation.
Besides, all types of the non-cylindrical cast-in-place piles
are constructed in dry working environment without any alkaline
mud or other pollutants left.
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Comparing with the current technology, the cast-in-place
pile of this invention has the following advantages:
- 1. Comparison between the flower-shape-pile of this
invention and the cylindrical pile
Take an ordinary cylindrical pile with diameter 800 mm
to compare with a flower-shape-pile with nearly same lateral
surface area, the S.P. 400-3x300 of the same length.
Referring to FIG. 1, 1 shows the cross section of the
flower-shape-pile, 2 shows the referring cross section of
a cylindrical pile with 800 mm diameter
| Pile Type | Specific Lateral Area (sq. m ) | Specific Volume (cu. m ) | Area Ratio | Volume Ratio |
| Cylindrical, 800 | 2.513 | 0.503 | 0.89 | 2.13 |
| S.P. 400-3x300 | 2.827 | 0.236 | 1.00 | 1.00 |
Above comparison shows that with the same length, when
the periphery frictional area of a cylindrical pile is only
89 % of that of the flower-shape-pile, but its volume
( concrete consumption ) is 2.13 times of that of the
flower-shape-pile. It means that the bearing capacity can
be improved about 10 % while the material consumption can
be dropped drastically. - 2. Comparison between the row-pile of this invention and the
conventional diaphragm wall
In foundation engineering practice, before construction
of an underground diaphragm wall of a deep pit, temporary
support must be set up to resist the horizontal pressure
from the back soil and water. A huge amount of construction
work and complicated technique are required. Referring
to the drawings . FIG. 3 illustrates a conventional
continuous underground wall body 8 with its pilot wall
9 ; FIG. 4 illustrates a temporary support consisted of
conventional soldier pile of lined up bulkhead piles 10
and water-tight plain concrete piles 11. Apparently, the
construction speed is low and cost high. By using the
method of this invention to construct diaphragm wall with
row-piles, the serious problem can be easily solved,
referring to FIG. 5, FIG. 6, and FIG. 7. A typical
procedure of the construction of the diaphragm wall may
be briefed as:
- 1 ) Drilling the boreholes of the row-piles, one by one
along the center line of diaphragm wall, then grouting concrete,
lowering the reinforcing cage with the built-in pre-embedded
parts 7 ( FIG. 2 ) into the borehole, and proceeding other
processes as FIG. 8 shows, the complete set of row-piles then
is built up;
- 2 ) Drilling and pouring concrete to form the water-tight
plain concrete piles 11;
- 3 ) As the concrete cured for several days, excavating the
soil in the pit layer by layer from the ground surface until
the first row of the pre-embedded parts has been fully exposed,
then welding the rigid connection parts 12 ( FIG. 5 );
- 4 ) Like steps going on, until all rigid connections are
made;
- 5 ) On the rim of the pit making the locking beam 13 and
the ground anchors 14 (FIG. 6 ) as required ( only on the rim
of the pit, at the middle span ).
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The adoption of the row-piles provided by this invention
does not need any temporary structure, neither bracings nor
web-beams, simplified the technique, effectively reduced the
labor , time, and cost. In addition, the safety in construction
can be better guaranteed. In its specific aspects the diaphragm
wall developed from the row-pile, the pile-and-wall integrate
design in foundation engineering, an advanced concept, can be
realized with tremendous economic gains. Another implicit
superiority to the conventional cylindrical pile is making fully
use of steel materials. In a cylindrical pile, the main
reinforcements should be evenly distributed along the
circumference to prevent steel cage from twisting, a large amount
of the steel bars close to the neutral zone of the pile for bending
resistance, failing to play their role. While the row-piles are
not circular in cross section, the steel cage could not twist
in the borehole, so the main reinforcements can be reasonably
distributed in the force-bearing surfaces and be fully used.
Almost about one-third of steel could be saved ( compared with
cylindrical piles ).
