SPECIFICATION
STEEL PILE DRIVING METHOD INVOLVING DEGASIFICATION PROCESS
Technical Field
[0001]
The present invention relates to a method of driving a steel pile, which employs
a flowable solidifying agent such as cement milk, and in particular to a method of driving
a steel pile, in which degasification is performed for the flowable solidifying agent at the
time of forming a foot protection portion.
The present application claims priority based on Japanese Patent Application No.
2010-084868 filed in Japan on April 1, 2010, the disclosures of which are incorporated
herein by reference in their entirety.
Background Art
[0002]
In this specification, the term "flowable solidifying agent" means various kinds
of flowable kneaded materials, including cement, which become solidified as time goes
by after being poured. For example, a flowable solidifying agent includes cement milk
having cement kneaded with water (additives or other chemical agents may be contained
in the cement milk), soil cement having cement milk kneaded with soil, mortar material
having cement milk kneaded with sand, and concrete material having cement milk
kneaded with sand (fine aggregate) and gravel (coarse aggregate).
Further, in this specification, the term "steel pile" means a steel material driven
into the ground such as a steel material for civil engineering or construction, which
includes H-shaped steels, steel sheet piles and steel pipes.
[0003]
The flowable solidifying agent is poured into a mold to form a structure body of
a building, or is injected or installed into the ground to form a structure body in the
2
ground. The flowable solidifying agent contains a relatively large number of bubbles
because air is confined in a space between the cement and water during the kneading,
pressure pumping, and pouring. If the flowable solidifying agent solidifies while
containing the bubbles, the solidified agent has a weaker strength than those without
containing the bubbles. Thus, it is preferable to perform degasification, more
specifically to remove the excess bubbles from the flowable solidifying agent after being
poured. In general, the degasification process for the flowable solidifying agent is
called "compaction." Compaction is performed by applying an appropriate vibration
energy to the flowable solidifying agent. The vibration enables the removal of excess
bubbles, so that a tight and high-strengthened solidified body can be obtained.
[0004]
As a general compaction vibration device, a rod-shaped vibrator, for example,
as described in Patent Document 1 is known. The rod-shaped vibrator generates
vibration having a frequency in the range of 116.7 Hz to 200 Hz and amplitude in the
range of about 0.5 mm to 1.25 mm (in this specification, the "amplitude" means one half
of a peak-to-peak vibration wave). Of vibration devices, the rod-shaped vibrator
provides relatively high frequency. In the high frequency range, the vibration energy
largely attenuates, which makes the vibration less likely to reach a long distance. This
means that the degasification effect of the rod-shaped vibrator is limited only in the
vicinity of the rod-shaped vibrator. With the rod-shaped vibrator, the degasification is
required to be performed by repeatedly inserting the rod-shaped vibrator into the
flowable solidifying agent at short intervals (for example, every 50 cm) while applying
the vibration energy. Thus, the flowable agent after being solidified is likely to have a
nonuniform degasified state, which makes it difficult to obtain a uniform and strong
solidified agent.
[0005]
Further, the rod-shaped vibrator is applicable only to the flowable solidifying
agent to be driven in a manner such that the surface thereof is exposed. Thus, the
3
rod-shaped vibrator cannot be used in the flowable solidifying agent to be driven into the
ground. Conventionally, there has been no effective manner of degasifying the flowable
solidifying agent used for forming an underground structure.
[0006]
As the structure formed in the ground and employing the flowable solidifying
agent, composite steel piles with soil cement have been well known. In a method of
driving a steel pile, a vibratory hammer is attached to a base end portion of a steel pile,
and vibration energy is applied to the steel pile, thereby driving the steel pile into the
ground while loosening the resistance of the ground. For a solid ground, a steel-pile
driving construction method employing water jet is known as described in Patent
Document 2.
[0007]
In the construction method described in Patent Document 2, plural
transportation piles are attached to the steel pile along the axial direction thereof, and
injection nozzles are disposed in the vicinity of the end portion of the steel pile. At the
time of driving the steel pile, highly pressurized water is injected from the injection
nozzles while applying the vibration with the vibratory hammer to excavate the ground,
thereby loosening the resistance of the ground. With the construction method
employing the water jet, the ground located below the steel pile is excavated, and hence,
it is impossible to obtain a force for supporting the end portion of the steel pile after the
steel pile is driven. To address this circumstance, after the steel pile is inserted to a
predetermined depth in the supporting layer, the flowable solidifying agent is injected
from the injection nozzle to solidify the agent, so that a foot protection portion is formed
in the vicinity of the end portion of the steel pile. The foot protection portion is a
solidified body of the flowable solidifying agent. With the foot protection portion, it is
possible to obtain the force for supporting the end portion of the steel pile.
Related Art Documents
4
ft
Patent Documents
[0008]
Patent Document 1: Japanese Examined Patent Application, Second Publication
No. S54-31608
Patent Document 2: Japanese Patent No. 3850802
Disclosure of the Invention
Problems to be Solved by the Invention
[0009]
The flowable solidifying agent used in the steel-pile driving construction
method described in Patent Document 2 also contains excess bubbles. Thus, in order to
form a much stronger foot protection portion, it is desirable to remove gas from the
flowable solidifying agent. However, the general rod-shaped vibrator cannot be applied
to the flowable solidifying agent to be poured into the ground. Thus, the idea of
removing gas from the flowable solidifying agent to be injected into and solidified in the
ground has not been thought of previously.
[0010]
On the inner and the outer surfaces at the end portion of the steel pile described
in Patent Document 2, raised portions or ribs are provided for the purpose of enhancing
adhesiveness with the foot protection portion. The raised portions or ribs transfer
vibration from the vibratory hammer at the time of injecting the flowable solidifying
agent to generate a pressure wave in the vicinity of the raised portions or ribs. This
pressure wave has an effect of providing a certain degree of degasification. However,
the flowable solidifying agent containing relatively large bubbles is continuously
supplied, and hence, the gas cannot be sufficiently removed only with the raised portions
or ribs of the steel pile. Further, with the construction method described in Patent
Document 2, after the steel pile reaches a designed depth (settled depth) and the driving
of the steel pile is stopped, operation of the vibratory hammer is stopped, and the
5
*
flowable solidifying agent is injected for a predetermined period of time. As a result,
the flowable solidifying agent becomes solidified in a state where the flowable
solidifying agent contains large-sized bubbles. This means that the strength of the foot
protection portion is reduced.
[0011]
In view of the circumstances described above, an object of the present invention
is to provide a method of driving a steel pile capable of removing gas from a flowable
solidifying agent in the ground to form a tight and uniform foot protection portion having
high strength.
Means for Solving the Problems
[0012]
In order to achieve the above-described object, the present invention employs
the following.
(1) An aspect of the present invention provides a method of driving a steel pile
using a vibratory hammer and a transportation pipe disposed along a longitudinal
direction of the steel pile to drive the steel pile into the ground, the method including:
injecting water from the transportation pipe while operating the vibratory hammer to
insert the steel pile in the ground up to a predetermined depth; injecting a flowable
solidifying agent from the transportation pipe while operating the vibratory hammer to
form a foot protection portion in the vicinity of an end portion of the steel pile; and
operating the vibratory hammer for a predetermined period of time after the steel pile
reaches a designed depth and the injection of the flowable solidifying agent is stopped,
thereby removing gas from the flowable solidifying agent.
(2) In the method of driving a steel pile according to (1) described above, the
vibratory hammer may be operated at a first amplitude set for the insertion in the
inserting of the steel pile and the forming of the foot protection portion, and the vibratory
hammer may be operated at a second amplitude set for removing gas in the removing of
6
*
gas from the flowable solidifying agent.
(3) In the method of driving a steel pile according to (1) or (2) described above, the
steel pile may have a line-shaped raised portion provided on an inner surface of the end
portion.
(4) In the method of driving a steel pile according to (1) or (2) described above, the
steel pile may have a planer rib raised portion provided on an outer surface of the end
portion.
Effects of the Invention
[0013]
According to the method described in (1) above, it is possible to remove gas
from the flowable solidifying agent in the ground, especially in the vicinity of the end
portion of the steel pile, so that a stronger structure can be formed in the ground.
[0014]
According to the method described in (2) above, the amplitude of the vibratory
hammer in the step of removing gas from the flowable solidifying agent is set
independently of the amplitude of the vibratory hammer in the step of inserting the steel
pile and the step of forming the foot protection portion, so that gas can be removed from
the flowable solidifying agent in a more favorable manner.
[0015]
According to the method described in (3) above, the line-shaped raised portion
provided on the inner surface of the end portion of the steel pile enables further
improvement in the degasification effect.
[0016]
According to the method described in (4) above, the planer rib raised portion
provided on the outer surface of the end portion of the steel pile makes it possible to
improve the adhesiveness of the foot protection portion with the steel pile, and to form a
foot protection portion having a larger size.
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Brief Description of the Drawings
[0017]
FIG. 1A is a side view illustrating a steel pile used in a method of driving the
steel pile according to an embodiment of the present invention.
FIG. IB is a plan view illustrating a steel pile used in the method of driving the
steel pile.
FIG. 1C is a partially sectioned perspective view schematically illustrating the
vicinity of an end portion of the steel pile.
FIG. ID is a partially enlarged view illustrating a planer rib raised portion
provided on the outer surface of the end portion of the steel pile.
FIG. IE is a sectional view taken along line A-A in FIG. ID.
FIG. 2 is a graph illustrating an effect of removing gas from a flowable
solidifying agent according to the method of driving the steel pile of the present
invention.
FIG. 3 is a diagram illustrating a method of selecting a vibratory hammer.
FIG. 4 is a diagram schematically illustrating a flow from a process (A) to a
process (G) in the method of driving the steel pile.
FIG. 5 A is a graph illustrating a change in depth of end position of the steel pile
with respect to time.
FIG. 5B is a table showing how processes are managed for samples 1 to 4.
Embodiments of the Invention
[0018]
Hereinbelow, a detailed description will be made of a method of driving a steel
pile according to an embodiment of the present invention.
[0019]
8
#
I The method of driving a steel pile according to this embodiment includes
I operating a vibratory hammer for a predetermined period of time after completion of
driving the steel pile, in other words, after the steel pile is positioned at a designed depth
\ (settled depth) and injection of a flowable solidifying agent is stopped, thereby removing
gas from the flowable solidifying agent existing in the vicinity of an end portion of the
steel pile in a non-solidified state. Conventionally, vibratory hammers have been used
merely to drive the steel pile. No attempt has been made so far to actively utilize
vibration energy of the vibratory hammer for the purpose of removing gas from the
flowable solidifying agent existing in the ground.
[0020]
The vibratory hammer is a vibration device having a frequency range and
amplitude range totally different from those of the rod-shaped vibrator described above.
The frequency of the vibratory hammer is lower, and the amplitude of the vibratory
hammer is larger as compared with those of the rod-shaped vibrator. Thus, the settings
of the frequency and the amplitude for degasification by the vibratory hammer are totally
different from those by the rod-shaped vibrator. The lower frequency makes the
vibration energy attenuate more gradually, and is advantageous in that vibration is likely
to reach a longer distance. The larger amplitude is advantageous in that larger vibration
energy can be obtained. By uniformly transferring the vibration energy to the entire
flowable solidifying agent to uniformly remove gas, uniformity in terms of strength can
be achieved in the solidified body.
[0021]
The flowable solidifying agent is compacted by performing degasification.
The wording "degasification" or "remove gas" and the wording "compaction" as used in
this specification are different only in terms of expression, and represent the same
phenomenon.
[0022]
4
If predetermined vibration energy is applied to a flowable solidifying agent
existing in a non-solidified state, cement particles adhered to each other are separated,
losing resistance to shearing force. This causes the flowable solidifying agent to be in a
liquid form, increasing the fluidity of the flowable solidifying agent and accelerating
degasification of the large bubbles contained between the cement particles, thereby
obtaining a compacted flowable solidifying agent. After being compacted, the flowable
solidifying agent solidifies to form a strong foot protection portion in the vicinity of the
end portion of the steel pile. With the method of driving the steel pile according to this
embodiment, the degree of strength of the foot protection portion improves as compared
with that formed through the method without performing degasification.
[0023]
The flowable solidifying agent has a characteristic in which fluidization is more
likely to occur as the frequency of movement of cement particles occurring in unit time
increases and the relative displacement (amplitude) between the cement particles
increases. Thus, in theory, by adjusting either or both of the frequency and the
amplitude, it is possible to adjust the degree of fluidization, in other words, the
degasification effect. With the general amplitude-variable vibratory hammer, it is true
that the frequency can be changed. However, it is the amplitude that can be changed
more easily and widely. Thus, it is possible to optimally insert the steel pile and form
the foot protection portion by operating the vibratory hammer with a first amplitude set
for the insertion at the time of inserting the steel pile, and operating the vibratory hammer
with a second amplitude set for the degasification at the time of removing gas from the
flowable solidifying agent.
[0024]
A raised portion provided at an end portion of the steel pile transfers vibration
from the vibratory hammer at the time of degasification to generate a pressure wave in
the vicinity of the raised portion. This pressure wave also has a degasification effect.
Thus, the raised portion has an effect of further enhancing the degasification effect obtained by the vibration from the vibratory hammer. [
[0025]
1. Basic mode of method of driving steel pile
Hereinbelow, a basic mode of the method of driving a steel pile including the
degasification step according to this embodiment will be described with reference to FIG.
1A to FIG. IE.
[0026]
FIG. 1A is a side view illustrating a steel pile, and FIG. IB is a plan view
illustrating the steel pile. FIG. 1C is a partially sectioned perspective view
schematically illustrating the vicinity of the end portion of the steel pile (foot protection
portion) after the completion of construction. FIG. 1D is a partially enlarged view
illustrating a planer rib raised portion provided on an outer surface of the end portion of
the steel pile. FIG. IE is a sectional view taken along line A-A in FIG. ID.
A steel pile 1 illustrated in FIG. 1A is a steel pipe pile. The present invention
is directed not only to a steel pipe pile but also, for example, to a steel pipe sheet pile and
an H-shaped steel pile. The outer diameter of the steel pile 1 is in the range, for
example, of 600 mm to 1500 mm.
[0027] i
The outer surface of the steel pile 1 is provided with plural transportation pipes
3 (four transportation pipes in the drawing) along the axial direction (in the longitudinal
direction) of the steel pile. The transportation pipe 3 may be attached on the inner
surface of the steel pile 1. Within the transportation pipe 3, a pipeline is provided for
pressure feeding of water or flowable solidifying agent. The end portion of the
transportation pipe 3 is located in the vicinity of the end portion of the steel pile 1. This
end portion is provided with an injection port 3a of an injection nozzle (not illustrated)
having an appropriate form. The injection port 3a has a diameter in the range, for
example, of 3 mm to 8 mm. A base end of the transportation pipe 3 is separated away
from the outer surface of the steel pile 1 in the vicinity of the base end of the steel pile 1,
and is connected with a device (not illustrated) disposed on or above the ground. This
device includes a device for switching water and the flowable solidifying agent, a device
for feeding water and the flowable solidifying agent, a tank, and a kneading device. The
transportation pipe 3 may be drawn from the steel pile 1 to the ground surface to be
removed in the final step of construction.
[0028]
Plural planer rib raised portions lb protruding radially may be attached on the
outer surface in the vicinity of the end portion of the pile body la. The planer rib raised
portions 1 b are attached in a manner such that a plate surface of each of the planer rib
raised portions lb is parallel to the axial direction of the steel pile. With the planer rib
raised portions lb described above, a foot protection portion having a larger diameter can
be effectively formed. The planer rib raised portions lb may have a rectangular shape
or a corner-cut rectangular shape (having a shape in which one or more corners are cut
off in the rectangular shape), for example. The number of the planer rib raised portions
lb is, for example, 2 to 5. The planer rib raised portions lb are arranged, for example,
in the circumferential direction of the steel pile 1 at equal angles as illustrated in FIG. IB.
[0029]
As illustrated in FIG. ID and FIG. IE, the planer rib raised portion lb is formed
by striped steel plates. On the surface of the striped steel plates, elongated small raised
portions lbl are arranged alternately at opposite angles to each other to form a
generally-reticular-shaped pattern as a whole. Each of the small raised portions lbl has,
for example, a length of 28 mm and a width of 4.5 mm. Note that the arrangement
pattern of the large number of small elongated raised portions lbl is not limited to the
example illustrated in the drawing.
[0030]
As illustrated in a sectioned portion of FIG. 1C, the inner surface of the end
portion of the pile body la may be provided with one or more line-shaped raised portions
12 5
(slip resistance, slip keeper) lc. The line-shaped raised portions lc illustrated in the
drawing are formed by plural ring-shaped raised portions arranged horizontally at
predetermined intervals. The line-shaped raised portions lc may be formed by spirally
shaped raised portions, rather than the plural ring-shaped raised portions.
[0031]
A foot protection portion CI formed in the vicinity of the end portion of the pile
body la in FIG. 1C is a solidified body of the flowable solidifying agent injected from
the transportation pipe 3. The foot protection portion CI is formed so as to extend from
a predetermined depth (maximum depth) D4 to a drawing depth Dl with respect to the
steel pile 1. In the example illustrated in FIG. 1C, the drawing depth Dl is located at
almost the same position as the upper end D2 of a supporting layer (interface between an
intermediate layer and the supporting layer). A designed depth (settled depth) D3,
which is a final position of the steel pile 1, is located above the predetermined depth D4.
The foot protection portion CI has a diameter larger than the steel pile 1. Part of the
flowable solidifying agent enters the inside of the steel pile 1, and solidifies, whereby the
foot protection portion CI is formed integrally with the end portion of the steel pile 1.
This makes it possible to obtain a force for supporting the end portion of the steel pile 1.
Note that the planer rib raised portion lb and the line-shaped raised portions lc are
provided for the purpose of enhancing the adhesiveness between the foot protection
portion CI and the steel pile 1, and improving the degasification effect.
[0032]
As described later, after the steel pile 1 is positioned at the designed depth
(settled depth) D3, supply of the flowable solidifying agent is substantially stopped, and
the vibratory hammer is caused to operate, thereby performing the degasification process,
in other words, the compaction process.
[0033]
As the flowable solidifying agent, it may be possible to employ cement milk
having cement kneaded with water (additives or other chemical agents may be contained
13 ; t
in the cement milk). The ratio of water relative to cement (W/C) falls in the range, for
example, of 50% to 150%.
[0034]
2. Theory of compaction of flowable solidifying agent with vibratory hammer

In the case where the flowable solidifying agent is compacted with the
rod-shaped vibrator on the ground, a high frequency in the range of about 116.7 Hz to
200 Hz is employed. If the vibration frequency is high, amplitude of the vibration
sharply attenuates with distance from the vibration source. Thus, in the case of using
the rod-shaped vibrator, compaction is performed on the entire flowable solidifying agent
by inserting the rod-shaped vibrator in plural positions (in general, about every 50 cm) of
the flowable solidifying agent. However, application of the rod-shaped vibrator to the
flowable solidifying agent existing in the ground is structurally impossible. Further, it
is difficult to dispose the rod-shaped vibrator at a desired position in the ground.
[0035]
On the other hand, the vibratory hammer is attached at the upper end of the steel
pile, in other words, above the ground. Vibration from the vibratory hammer transfers
through the steel pile to the end portion of the steel pile existing in the ground. In this
embodiment, in the case where compaction is performed with the vibratory hammer in
the ground, low frequency in the range of about 11.7 Hz to 18.3 Hz is employed. If the
vibration frequency is low, the vibration is less likely to attenuate, and reaches a long
distance from one vibration source. In this respect, it is reasonable to employ the
vibratory hammer to perform compaction of the flowable solidifying agent existing in the
ground.
[0036]
Next, in connection with the compaction performance, the rod-shaped vibrator
is numerically compared with the vibratory hammer used in the method of driving a steel
pile according to this embodiment. The compaction performance for the flowable
14
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solidifying agent with the vibration device can be evaluated using vibration acceleration
n and vibration compaction energy Ec. By calculating these values, it is possible to
compare both devices in terms of compaction performances. Note that the term
"vibration compaction energy" means vibration energy used for the compaction.
[0037]
Table 1 shows comparison results in terms of the vibration acceleration n and
the vibration compaction energy Ec between a general rod-shaped vibrator and the
vibratory hammers used in the method of driving the steel pile according to this
embodiment. Vibratory hammers in examples have motor outputs of 90 kW, 120 kW,
180 kW, and 240 kW. Selection of appropriate vibratory hammers will be described
later. The vibration acceleration n and the vibration compaction energy Ec were
calculated using parameter values and expressions shown in the table. The character g
represents acceleration of gravity (9.81 m/s ).
15
[0038]
[Table 1]
G eneral V ibr atory ham m er (Ex ampl e s)
Parameter Unit rod-shaped 1 1 1
vihrator 90 kW 120 kW 180 kW 240 kW
1.167 x 102
Frequency f Hs to 1.830x10 1.630x10 1.330x10 1.170x10
2.000 xlO2
:
Angular 7.328 xlO2
frequency sec-1 to 1.149 xlO2 1.023 x 102 8.352x10 7.347x10
(p[=2ufj 1.256 xlO3 | | |
Amplitude A mm 1.250 5.000
Vibration 6.712 xlO2
acceleration a m/ s2 to 6.601x10 5.233x10 3.488x10 2.699x10
[=Aco2xlQ-3] 1.972 xlO3
Vibration 6.842x10
acceleration T\ G to 6.729 5.334 3.556 2.751
[= a/g] I 2.010 xlO2 I | | |
Ratio i^ of 75:1
vibration accelerationT| (2.010 x 102/2.751 = 73.1)
Vibrating
mass kg 5.000 6.000 xlO3 7.950 x 103 1.180x10* 1.995x10*
S.
Vibration load Wf
r _, ,„,, kN 4.905xl0"2 5.886x10 7.799x10 1.158 x 102 1.957 xlO2
[^W^gxlO^]
Eccentric ^ ^ ^ -, ^
. „ N-m 6.131 x 10"2 2.943 xlO2 3.899 x 102 5.788 x 102 9.785 xlO2
moment K
Vibration
generating
f o r c e P kN 3.356to9.858 3.961 xlO2 4.159xl02 4.116 x 102 5.384xl02
[= (K to2/g) x 10"3]
V ibration
compaction 4256 *10"3
.„«<*,* kNm to 2- 2 7 5 2M9 2-fi37 3.671
energy E.(.
[= A(Wf + P ^ x 10"3] 1.239x10"
RatioECRof
Vibration 1:180
compaction (2.275/1.239 x 10"2 = 176.4)
energyEc
[0039]
In Table 1, vibrating mass Wv of the vibratory hammer corresponds only to the
vibrating mass of the vibratory hammer. For the driving of the steel pile, total vibrating
mass obtained by adding the vibrating mass of the vibratory hammer to the vibrating
mass of the steel pile is employed as the vibrating mass Wv. In this embodiment, only
the vibrating mass of the vibratory hammer is employed to compare compaction
performances of the vibratory hammer itself as a vibration device with those of the
rod-shaped vibrator.
[0040] j
As for vibration acceleration t|, the rod-shaped vibrator having high frequency
has advantageous values as compared with the vibratory hammer. Thus, for the
vibration acceleration n, a vibration acceleration ratio nr between the rod-shaped vibrator
and the vibratory hammer is obtained in a manner such that this ratio is maximum within
a target frequency range. The vibration acceleration ratio nr was about 75:1. More
specifically, the vibration acceleration r\ of the rod-shaped vibrator is 75 times that of the
vibratory hammer at the maximum.
[0041]
Further, for vibration compaction energy Ec, the vibratory hammer having a
large vibrating mass has advantageous values as compared with the rod-shaped vibrator.
Thus, for the vibration compaction energy Ec, a vibration compaction energy ratio Ecr
between the rod-shaped vibrator and the vibratory hammer is obtained in a manner such
that this ratio is minimum within a target frequency range. The vibration compaction
energy ratio Ecr was about 1: 180. More specifically, the vibration compaction energy
Ec of the vibratory hammer is at least 180 times that of the rod-shaped vibrator.
[0042]
On the basis of the comparison results with the rod-shaped vibrator, it can be
understood that, with the vibratory hammer, the advantage of the vibration compaction
energy Ec compensates for the disadvantage of the vibration acceleration n, and the
vibratory hammer can achieve the compaction performances equal to or higher than those
obtained by the rod-shaped vibrator. This is because the amplitude A of the vibratory
hammer is set to values higher than the "ordinary amplitude." The "ordinary
amplitude" of the vibratory hammer means values set for inserting the steel pile. In the
example in Table 1, the minimum required amplitude A of the vibratory hammer set for
*
the compaction is 5 mm. Such a large amplitude can be obtained only with low
frequency and large eccentric moment.
[0043]
The method of driving a steel pile according to this embodiment employs the
vibratory hammer that can generate vibration with an amplitude capable of dealing with
the degasification process and that can change this amplitude from the amplitude suitable
for the inserting process to the amplitude suitable for the degasification process.
[0044]

Next, the time for vibration-forced degasification required for the vibration
compaction will be discussed.
In general, the rod-shaped vibrator is inserted at about 50 cm intervals, and
compaction time te for each insertion is about 15 sec to 20 sec. Degasification time tv
with the vibratory hammer can be obtained from the following expression by using
compaction time ts concerning the rod-shaped vibrator, a ratio r|r of the vibration
acceleration and a ratio Ecr of the vibration compaction energy shown in Table 1.
tv = a-tB-nr/Ecr
tv: time for vibration-forced degasification with vibratory hammer (second)
a: coefficient of margin-adding time
r|r: vibration acceleration ratio
te: time for vibration-forced degasification with rod-shaped vibrator (second)
Eer: vibration compaction energy ratio
[0045]
The character a represents a coefficient multiplied for obtaining an additional
time for the vibration-forced degasification, and 2 to 3 is sufficient for the coefficient.
Table 2 shows calculation results. Values of vibration acceleration ratio r|r and
vibration compaction energy ratio Ecr used in calculation in Table 2 are obtained by
taking into account that about 10% loss of vibration acceleration n occurs due to
I
f
fiictional force between the vibratory hammer and soil. The rod-shaped vibrator is
inserted directly into the flowable solidifying agent, and hence, the vibration compaction
energy is transferred in full. On the other hand, the vibratory hammer is located on the
ground and the flowable solidifying agent exists in the ground, which inevitably causes
loss due to friction with the soil during transfer of the vibration. Thus, the vibration
compaction energy generated by the vibratory hammer is not transferred in full to the
flowable solidifying agent, and is transferred with about 10% loss.
[0046]
On the basis of the results shown in Table 2, the time required for the
degasification with the vibratory hammer falls between about 19 seconds and 29 seconds.
Thus, about 30 seconds of degasification is considered to be adequate for degasifying
with the vibratory hammer at the maximum.
[0047]
[Table 2]
General Vibratory
Parameter Unit rod-shaped hammer
vibrator (240 kW)
Frequency f Hz 2.000 x 102 1.170x10
Vibration
acceleration 80:1
ratio 1^*1
Vibration
compaction . , , ,
1:165 i
energy
ratio Er- *1
added sec tB 20 t, 29
time tg, ty v
* 1: Value obtained by taking into account ab out 10% loss of vibtarotory hammer
occurring due to frictional force with soil in the value in Table 1
0048]
FIG. 2 is a graph conceptually illustrating the effect of compacting the flowable
solidifying agent with vibration generated by the vibratory hammer. The horizontal axis
represents the time required for vibration-forced degasification. The vertical axis
represents density of the fiowable solidifying agent. By applying vibration compaction
energy, bubbles are removed from the fiowable solidifying agent, and the density of the
fiowable solidifying agent increases. The density-increasing curve varies to some
extent depending on various conditions such as viscosity of the fiowable solidifying
agent. However, by applying vibration with a predetermined amplitude, the density
reaches the upper limit within about 30 seconds at the longest from the start of applying
the vibration. In other words, the compaction can be completed. [0049]

At least about 3 mm of amplitude is empirically necessary to insert the steel pile
with the vibratory hammer, and the amplitude is generally set in the range of 3 mm to 6
mm. On the other hand, in order to enhance the effect of removing gas in the fiowable
solidifying agent existing in the ground with the vibratory hammer, it is preferable to set
the amplitude in the range of 5 mm to 10 mm, at which amplitude is not conventionally
set. This is because high vibration compaction energy is required.
Thus, in the method of driving the steel pile according to this embodiment, a
vibratory hammer capable of changing amplitude in the range of 3 mm to 10 mm is
selected.
[0050]

It is assumed that the frictional force of soil is 1 when the vibration acceleration
n is 0. Further, it is also assumed that the soil in this case is clay. Clay is the most
difficult soil to reduce the frictional force with vibration. If a water jet is not employed,
the frictional force of the soil empirically decreases to 0.2 or less in the case where the
vibration acceleration r\ is 5G or more. If a water jet is employed, the frictional force of
the soil empirically decreases to 0.1 or less in the case where the vibration acceleration n
is 3.5G or more. The method of driving the steel pile according to this embodiment
20
employs the water jet for inserting the steel pile. Thus, it is sufficient to set the ;
vibration acceleration n of the vibratory hammer necessary to insert the steel pile to 3.5G
or more. The upper limit of the vibration acceleration n is set to about 10G on the basis I
of the upper limits of the amplitude and the frequency. Thus, the vibration acceleration j
n at the time of insertion is set in the range of 3.5G to 10G. j
[0051] I

The method of driving the steel pile according to this embodiment employs one j
vibratory hammer, and performs three processes including a process of inserting the steel
pile into the ground (first process, inserting process), a process of injecting the flowable
solidifying agent (second process, foot protection portion-forming process), and a process ;
of removing gas from the flowable solidifying agent (third process, degasification
process). Thus, it is necessary to select a vibratory hammer that satisfies the conditions
required for all the processes. >
[0052] j
Next, steps of (a) to (e) concerning selection of an appropriate vibratory hammer will be described as an example of a case where a steel pile under a specific
standard is driven into the ground having a specific soil characteristic through the method f
of driving the steel pile according to this embodiment. Note that the standard for the
steel pile given as an example includes an outside diameter cp of 1000 mm, a plate !
thickness of 14 mm, a length of 20 m, and a mass in unit length of 340 kg/m.
[0053] j
(a) Determination of frequency
The frequency of the vibratory hammer is determined to be one frequency in the
range of 11.7 Hz to 18.3 Hz (specific type is not yet determined at this point in time).
[0054]
(b) Calculation of mass of steel pile
21
It
On the basis of the mass in unit length of 340 kg/m and the length of 20 m, the
mass Wp (kg) of the steel pile is calculated as follow:
Mass Wp (kg) of the steel pile = 340 x 20 = 6800
[0055]
(c) Calculation of resistance value at the time of inserting steel pile
The characteristic of the soil located at the steel pile being inserted can be
obtained from a soil-boring log indicating depth and N values. On the basis of the
soil-boring log, a resistance R against insertion can be calculated at a desired embedded
depth of the steel pile (inserted length in the ground) through the following expression:
Resistance R against insertion = 300N-AP + (10N-N;-LC + 2N;-LS)-AS
N: Maximum N value
Ap: Cross-sectional area (m ) of enclosed end portion of steel pile
N;: Average N value of depth of steel pile being inserted
Lc: Depth (m) of steel pile inserted into clay soil
Ls: Depth (m) of steel pile inserted into sandy soil
As: Circumferential length (m) of steel pile
By substitution of each parameter, which is an example, the resistance R against
insertion can be obtained as follow:
Resistance R (kN) against insertion = 300 x 50 x 0.79 + (10x2x11.7+ 10x5
x 1.3+ 2 x 22.5 x 2.0) x 3.14 =13071
[0056]
(d) Selection of vibratory hammer type
FIG. 3 is a known "vibratory hammer selection diagram based on weight."
The type of vibratory hammer is selected from FIG. 3 on the basis of the mass Wp of
steel pile of 6800 kg and the resistance R against insertion of 13071 kN calculated in (b)
and (c) above. In this example, the vibratory hammer having a motor output of 180 kW
is selected.
[0057]
22
(e) Examination of appropriateness of specific vibratory hammer and Decision of
amplitude in each process
It was examined whether the vibratory hammer with the motor output of 180
kW has specifications applicable to the first process to the third process in the method of
driving the steel pile according to this embodiment, and on the basis of the examination ;
result, amplitude A suitable for each of the processes is set.
[0058]
(e-1) Setting for first process
Table 3 shows methods of examining whether the specified type of vibratory
hammer is applicable to the method of driving the steel pile according to this
embodiment, and in particular to the first process. The upper half of Table 3 shows
parameters indicating specifications of the specified type, and mass Wp of the steel pile.
The lower half of Table 3 shows examination items and examination results.
[0059]
[Table 3]
Specifications of vibratory hammer (180 kW) and steel pile mass <
Parameter Unit
Frequency f Hz 13.3
Angular frequency 5 mm) required for degasifi cation in third process 8.6 mm OK
A ^ = K^[(Wv+Wp)-g]xlQ3
Satisify vibration acceleration T) (>3.5G) for inserting steel pile
in first process 3.5 G OK
T) = 3.5
Satisify vibration acceleration r\ (> 3.5G) for inserting steel pile
in first process, and satisfy amplitude A (> 3mm) 4.92^5 mm OK
A=T) x g x 103/co2
[0060]
23
In the examination, it is first determined whether the maximum amplitude of the
vibratory hammer satisfies the amplitude necessary for degasification in the third step.
This is the most important requirement of the method of driving the steel pile according
to this embodiment, and hence, is examined first. The maximum amplitude Amax
calculated on the basis of the maximum value Kmax of the eccentric moment K is 8.6 mm.
This satisfies the amplitude range of 5 mm to 10 mm, which is required for performing
degasification in the ground in the method of driving the steel pile according to this
embodiment.
Next, examination was made to determine whether the amplitude A calculated
on the basis of 3.5G of the minimum acceleration required for insertion employing the
water jet in the first process falls within the amplitude range of 3 mm to 6 mm set for the
insertion. The amplitude A is about 5 mm, and satisfies the amplitude range for the
insertion.
As described above, it was examined whether this type of vibratory hammer is
applicable to the method of driving the steel pile according to this embodiment, and the
amplitude A appropriate for the first process is determined.
[0061]
(e-2) Setting for second process
In the second process, the water jet is switched into the flowable solidifying
agent, and the flowable solidifying agent is injected. In this second process, the
vibratory hammer operates with the same frequency and amplitude as those in the first
process.
[0062]
(e-3) Setting for third process
In the third process, the injection of the flowable solidifying agent is basically
stopped, and only the vibratory hammer operates to perform degasification. The same
frequency is applied. The amplitude A is set to an appropriate value of not less than the
minimum amplitude of 5 mm required for the degasification but not more than the
24 i
maximum amplitude Amax. For example, by setting the eccentric moment K to the maximum eccentric moment Kmax, the amplitude of 8.6 mm is obtained. At this time,
the vibration acceleration r| is 6.1G. The degasification period of time is 30 seconds at
the maximum.
[0063]
3. Embodiment of the method of driving steel pile
Next, the method of driving the steel pile, which includes the degasification
process, will be described with reference to FIG. 4. Processes (A) to (G) in FIG. 4
schematically illustrate an example of a method of driving a steel pile in accordance with
the method of driving the steel pile according to this embodiment.
This method includes a first process (process (A) and process (B) in FIG. 4) of
injecting water from the transportation pipe 3 while operating the vibratory hammer 2 to insert the steel pile 1 up to the predetermined depth D4, a second process (process (C) to
process (E) in FIG. 4) of injecting the flowable solidifying agent from the transportation
pipe 3 while operating the vibratory hammer 2 to form the foot protection portion in the
vicinity of the end portion of the steel pile 1, and a third process (process (F) in FIG. 4)
of operating the vibratory hammer for a predetermined period of time after the steel pile
is positioned at the designed depth (settled depth) D3 and the injection of the flowable
solidifying agent is stopped, thereby removing gas from the flowable solidifying agent.
[0064]

31
CLAIMS
1. A method of driving a steel pile using a vibratory hammer ^nd a transportation
pipe disposed along a longitudinal direction of the steel pile to drive the steel pile into a
ground, the method including: i
injecting a water from the transportation pipe while operating the vibratory
hammer to insert the steel pile into the ground up to a predetermined depth; -^
' " . "" injecting a flowable solidifying agent from the transportation pipe while
operating the vibratory hammer to form a foot protection portion in a vicinity of an end
portion of the steel pile; and
. > operatingthe vibratory hammer for a predetermined period of time after the steel
pile reaches a designed depth and the injection of the flowable solidifying agent is
stopped, thereby removing gas from the flowable solidifying agent.
2. The method of driving a steel pile according to Claim 1, wherein
- in the inserting of the steel pile and the forrning of the foot protection portion,
the vibratory hammer is operated at a first amplitude set for the insertion, and
in the removing of gas from the flowable solidifying agent, the vibratory
i • •
hammer is'operated at a second amplitude set for removing gas. , ,
3. The method of driving a steel pile according to Claim 1 or 2, wherein
the steeji'pile has a line-shaped raised portion provided on an inner surface of the
end portion.
4. The method of driving a steel pile according to Claim 1 or 2, wherein'
the steel pile has a planer rib raised portion provided on an outer surface of the
end portion.