JPH11209979A - Method for installing pile in poor subsoil and pile-driving cap for use therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the overall period and cost of construction work when constructing a structure on poor subsoil, while preventing damage to the structure and piles that may be caused by liquefaction. SOLUTION: A pile-driving cap 1 is almost cylindrical as a whole, and is formed with a driving surface 2 on its upper surface which is struck by a hammer, and with a recess part 3 in its lower surface into which the head of a pile is fitted. In this case, a step 5 is formed on the inner surface of the recess part 3, and the front side of the step 5 is formed into a large-diameter recess part 6 into which the head of a large-diameter pile is fitted, while the rear side of the step 5 is formed into a small-diameter recess part 7 into which the head of a small-diameter pile is fitted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing a pile driven into soft ground, particularly to liquefied ground, and a pile driving cap used for the pile driving operation.

[0002]

2. Description of the Related Art When seismic force acts on a sandy ground where the groundwater level is shallow and loose, a so-called liquefaction phenomenon occurs in which the pore water pressure between particles rises and the shearing resistance decreases significantly.
It is well known that when such a liquefaction phenomenon occurs, the structure constructed on the ground surface collapses very easily.

Therefore, it is necessary to prevent liquefaction of such liquefied ground by performing ground improvement by a method such as a sand compaction method, a crushed stone drain method or a rod compaction method.

[0004]

However, since such ground improvement must be performed in advance, there has been a problem that the construction period is long and the cost is high.

[0005] When a high-quality support layer exists deep underground, it is conceivable that a pile is driven into the support layer so as to penetrate the liquefied ground and the structure is supported by the pile. Even in such cases, if the shear resistance of the ground near the surface layer is extremely reduced due to liquefaction, the seismic horizontal force acting on the structure must be borne only by the pile, and the pile body, especially the pile head There has also been a problem that there is a risk of breakage in the part.

The present invention has been made in view of the above circumstances, and when constructing a structure on soft ground, especially liquefied ground, the structure and piles are prevented from being damaged due to liquefaction and the entire structure is prevented. It is an object of the present invention to provide a pile construction method in soft ground capable of shortening or reducing the construction period and cost, and a pile driving cap used therefor.

[0007]

In order to achieve the above object, a method for constructing a pile in soft ground according to the present invention is, as set forth in claim 1, characterized in that a step formed on an inner surface of a concave portion of a pile driving cap is formed. With the pile head of the small diameter portion fitted in the back side, the small diameter portion is driven into the ground using a driving surface formed on the opposite side of the pile driving cap, and the small diameter portion is brought to a predetermined depth. After driving, the cap for pile driving is removed, and a large diameter portion is connected to a pile head of the small diameter portion via a predetermined connecting portion, and the pile head of the large diameter portion is formed on the pile driving cap. The large-diameter portion is driven into the ground using the driving surface in a state of being fitted on the near side of the step.

According to a second aspect of the present invention, there is provided a pile driving cap in which a recess into which a pile head is fitted is formed on one side and a driving surface is formed on the other side. In the cap for use, a step is formed on the inner surface of the recess, the front side of the step is a large-diameter recess for fitting the pile head of the large-diameter portion, and the deep side of the step is the small-diameter portion of the pile. This is a small-diameter recess for fitting the head.

The method for constructing a pile in soft ground according to the present invention and the pile driving cap used therefor are applied to a ground in which a soft layer, particularly a liquefied layer, is distributed on a support layer. Of the small-diameter portion driven into the lower ground area, the diameter is appropriately determined based on the cross-sectional design usually performed as a pile for supporting the structure, but for the large-diameter portion driven into the upper ground area, Make the diameter larger than the diameter of the small diameter part. The diameter of the large-diameter portion is appropriately determined in consideration of the target compaction strength of the soft layer, the driving pitch of the pile, and the magnitude of the earthquake shear force that the pile should bear in the event of liquefaction. Determine. For the connection,
The pile diameter is formed, for example, in a truncated cone shape so that the pile diameter continuously changes between the small diameter portion and the large diameter portion.

On the other hand, a step is formed on the inner surface of the concave portion of the pile driving cap. The front side of the step is a large-diameter concave portion for fitting the pile head of the large-diameter portion, and the rear side of the step is formed. Is a concave portion for small diameter for fitting the pile head of the small diameter portion.

In order to drive the soft ground pile composed of the small-diameter portion, the connecting portion and the large-diameter portion into the ground using the pile driving cap while interconnecting the soft ground piles on site, as described above. First, the pile head of the small diameter portion is fitted into the deep side of the step formed on the inner surface of the concave portion of the pile driving cap. And
In this state, the small diameter portion is driven into the ground to a predetermined depth using the driving surface formed on the opposite side of the pile driving cap.

Next, the pile driving cap is once removed, and the large diameter portion is connected to the pile head of the small diameter portion via a predetermined connecting portion.

Next, the removed cap for pile driving is used again as a cap for pile driving of the large diameter portion. That is, the pile head of the large diameter portion is driven into the ground in a state where it is fitted on the near side of the step formed in the cap for pile driving in the same manner as when driving the small diameter portion.

Thus, in the construction stage,
The large diameter portion is driven into the surrounding soft layer, in particular, the liquefied layer, in such a manner as to spread the layer together with the spreading action of the connecting portion. As a result, the liquefied layer is compacted, and the occurrence of a liquefaction phenomenon when an earthquake is encountered is prevented. In addition, when there is no concern about liquefaction, for example, even when the groundwater level is deep but the soft layer consists of a loose sand layer, the sand is compacted when the large diameter part is driven in. To increase.

On the other hand, when an earthquake is encountered after construction,
Liquefaction is prevented beforehand by the compaction action of the liquefied layer by the connecting portion and the large diameter portion as described above, and the earthquake resistance is improved by an increase in ground shear resistance due to the compaction action of the sand layer.

[0016] Even if the liquefaction phenomenon cannot be avoided due to insufficient compaction or the increase in the ground shear resistance is not sufficient, the shear resistance just below the upper structure is also required. The lack of force will be borne by the large-diameter portion having the increased cross section, and damage to the pile body, particularly the pile head, will be prevented beforehand.

Further, one pile driving cap can be used also for driving the small diameter portion and the large diameter portion, and the labor and cost for separately preparing caps corresponding to the respective diameters can be omitted.

The material and structure of the small-diameter portion, the connecting portion and the large-diameter portion of the liquefied ground pile are optional. Steel, RC, PC
Although it may be appropriately selected from such as, but in the present invention, since the connection at the site is premised, each of the above-described parts is configured by a steel pipe,
The parts are preferably interconnected by field welding. The small-diameter portion, the connecting portion, and the large-diameter portion may be transported to the site in a disassembled state, and thereafter, may be sequentially connected upward by welding or the like in accordance with the progress of the driving. Alternatively, the lower end of the large diameter portion may be connected in advance at a factory.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of a method for constructing a pile in soft ground and a pile driving cap used in the method according to the present invention will be described with reference to the accompanying drawings. It is to be noted that the same reference numerals are given to components and the like that are substantially the same as those in the conventional technology, and description thereof will be omitted.

FIG. 1 is an overall view and a cross-sectional view showing a pile driving cap according to this embodiment. As can be seen from the figure, the pile driving cap 1 of this embodiment has a substantially cylindrical shape as a whole, forms a driving surface 2 on which a hammer is struck on the upper surface, and a pile head is fitted on the lower surface. A recess 3 is formed.

The pile driving cap 1 itself is made of, for example, steel, and the driving surface 2 is provided with a cushion 4 made of wood or the like.

On the other hand, a step 5 is formed on the inner surface of the recess 3, and a front side of the step is a large diameter recess 6 for fitting a pile head of a large diameter pile, and a rear side of the step 5. Is a concave portion 7 for a small diameter for fitting the pile head of the small diameter pile. In addition,
As shown in the figure, cushions 4a and 4b are attached to the step 5 where the pile head of the large diameter pile comes in contact and the deep side of the concave portion 7 for small diameter where the pile head of the small diameter pile comes in contact, respectively, as shown in FIG. Good to put.

FIG. 2 is an exploded perspective view showing a soft ground pile driven into the ground using the pile driving cap 1. As can be seen from the figure, the soft ground pile 11 includes a small-diameter portion 12 driven into a lower region of the ground, a large-diameter portion 14 driven into an upper-region of the ground, and a small-diameter portion 12 and a large-diameter portion 14. It is composed of a frusto-conical connecting part 13 which is connected to the small diameter part 12 and the large diameter part 14 so that the diameter changes continuously.

In the soft ground pile 11, the small-diameter portion 12, the connecting portion 13, and the large-diameter portion 14 are preferably made of, for example, steel pipes, and are preferably delivered to the site in a disassembled state.

The diameter of the small diameter portion 12 is appropriately determined based on a cross-sectional design usually performed as a pile for supporting a structure. Note that the lower end may not be an open type as shown in FIG.

The large diameter portion 14 is made thicker than the small diameter portion 12, and the degree thereof depends on the density of the liquefied layer, the target compaction strength, the driving pitch of the pile, or the case where liquefaction occurs. It is determined as appropriate in consideration of the magnitude of the shear force during an earthquake that the piles should bear.

A pile driving cap 1 according to the present embodiment and a method of constructing a pile in soft ground using the same are shown in FIG.
As shown in (a), the present invention is applied to a ground 23 in which a liquefied layer 22 as a soft layer is distributed on a support layer 21.

To drive the soft ground pile 11 into the ground 23 using the pile driving cap 1 of the present embodiment, FIG.
First, the pile head of the small-diameter portion 12 of the soft ground pile 11 is fitted into the small-diameter concave portion 7 on the deep side of the step 5 formed on the inner surface of the concave portion 3 of the pile driving cap 1. Then, in this state, the small-diameter portion 12 is driven into the ground 23 to a predetermined depth using the driving surface 2 formed on the opposite side of the pile driving cap 1 as shown in FIG.

Next, the pile driving cap 1 is once removed from the small diameter portion 12 of the soft ground pile 11, and then the large diameter portion 14 is connected to the pile head of the small diameter portion via the connecting portion 13.

Next, the removed pile driving cap 1 is used again as the pile driving cap of the large diameter portion 14.
That is, as shown in FIG.
The pile head of the large-diameter portion 14 is fitted into the large-diameter concave portion 6 located on the front side of the step 5 formed in the above-mentioned step, and the driving surface 2 formed on the opposite side of the pile driving cap 1 in such a state is used. Part 1
4 is driven into the ground 23 to a predetermined depth as shown in FIG.

In this way, in the construction stage,
The large diameter portion 14 is driven into the liquefied layer in such a manner as to spread the surrounding liquefied layer 22 in combination with the spreading action of the connecting portion 13. As a result, the liquefied layer 22 is compacted.

On the other hand, when an earthquake is encountered after construction, the liquefaction layer 22 is compacted by the connecting portion 13 and the large-diameter portion 14 as described above, thereby preventing liquefaction from occurring. In the unlikely event that the compaction is insufficient, the occurrence of the liquefaction phenomenon cannot be avoided. As a result, even if the shear resistance of the liquefied layer 22 decreases, the decrease in the shear resistance is caused by the increase in the thickness of the cross section. Diameter 14 bears.

Further, the cap 1 for pile driving has a small diameter portion 12.
And the driving of the large diameter portion 14.

As described above, according to the pile construction method and the pile driving cap 1 used in the soft ground according to the present embodiment, at the construction stage, the large-diameter portion 14 and the connecting portion 13 are expanded and pushed. The liquefaction layer 22 is compacted. Therefore, it is possible to prevent the occurrence of liquefaction when an earthquake is encountered without separately performing liquefaction countermeasure work that causes high cost and a long construction period. In addition, although the diameter corresponding to the liquefied layer was made large, the diameter of the other parts was small enough to fulfill the function of the original pile, so it was driven in rather than making the whole cross section thick. Not only is it easy to operate, but also the effect of minimizing the cost increase due to the enlargement of the cross section is exhibited.

When an earthquake is encountered after construction,
Even if the compacting action of the liquefied layer 22 by the connecting portion 13 and the large-diameter portion 14 as described above is insufficient and liquefaction cannot be prevented, the decrease in the shear resistance of the liquefied layer 22 is as follows. The large diameter portion 4 having an increased cross section bears the burden.

Therefore, the horizontal force at the time of the earthquake from the upper structure acting on the pile head of the soft ground pile 11 is sufficiently supported by the shear resistance and the bending resistance of the large diameter portion 14, and the pile body, especially It is possible to prevent damage at the pile head.

The area where the soft ground pile 11 is driven is prevented from liquefaction by its action, while if the surrounding ground that has not undergone ground improvement liquefies, the input seismic wave from the surrounding ground is reduced. It can be expected that the surrounding ground can function as a damper that attenuates the roll of the ground immediately below the upper structure.

Further, according to the method of pile construction in soft ground and the pile driving cap 1 used in this embodiment, one pile driving cap 1 is also used for driving the small-diameter portion 12 and the large-diameter portion 14. As a result, it is possible to save labor and cost for separately preparing caps corresponding to the respective diameters.

In the present embodiment, the connecting portion 3 is formed in a truncated conical shape so that the resistance at the time of driving is reduced as much as possible. Any shape may be used as long as the shape is not discontinuous and gradually increases from the portion 2 to the large diameter portion 4.

In the present embodiment, the present invention is applied to the liquefied layer. However, if there is no concern about liquefaction, for example, if the soft layer is formed of a loose sand layer, the present invention is applied to the soft layer. It can be applied in the same manner as in the above-described embodiment. According to such a configuration, the ground shear resistance of the loose sand layer can be increased by the compaction action at the time of driving, and even if the ground shear resistance cannot be sufficiently increased, it is not sufficient. Since the large diameter portion bears the burden, the earthquake resistance of the ground can be improved anyway.

[0041]

As described above, according to the method for constructing a pile on soft ground according to the first aspect of the present invention and the cap for driving a pile according to the second aspect, at the construction stage, the large-diameter portion and the connecting portion are connected. The soft layer is compacted by the spreading action. Therefore, while preventing the occurrence of the liquefaction phenomenon, it becomes possible to increase the shear resistance of the ground, and even if the compaction is not sufficient, the shortage of the shear resistance is reduced. Since the large-diameter portion with increased cross section bears, the horizontal force at the time of the earthquake from the upper structure acting on the pile head of the soft ground pile is sufficiently supported by the shear resistance and bending resistance of the large-diameter portion, It is possible to prevent the pile body, particularly the pile head, from being damaged. Further, one pile driving cap is also used for driving the small-diameter portion and the large-diameter portion, so that labor and cost for separately preparing caps corresponding to the respective diameters can be omitted.

[0042]

[Brief description of the drawings]

FIG. 1 is a view showing a pile driving cap 1 according to the present embodiment, wherein (a) is an overall perspective view and (b) is a cross-sectional view.

FIG. 2 is an exploded overall perspective view of a pile 11 for soft ground.

FIG. 3 is a view showing a work procedure of a method of constructing a pile in soft ground using the pile driving cap 1, (a) is a cross-sectional view of the ground including a liquefied layer, and (b) is a pile driving method. Sectional drawing which showed the mode that the small diameter part 12 of the liquefaction ground pile 11 was fitted in the cap 1, and (c) is sectional drawing which showed the mode that the small diameter part 12 was driven into the ground 23. FIG.

FIG. 4 is a diagram showing a work procedure of a method for constructing a pile in soft ground using the pile driving cap 1 continuously;
(a) is a sectional view showing a state in which the large diameter portion 14 of the soft ground pile 11 is fitted into the pile driving cap 1, and (b) is a large diameter portion 1.
Sectional drawing which showed a mode that 4 was driven into the ground 23. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pile driving cap 2 Driving surface 3 Depression 5 Step 6 Large diameter depression 7 Small diameter depression 11 Soft ground pile 12 Small diameter part 13 Connection part 14 Large diameter part 22 Liquefied layer (soft layer)

Claims (2)

[Claims] 1. A driving surface formed on an opposite side of the pile driving cap in a state where a pile head of a small diameter portion is fitted into a deep side of a step formed on an inner surface of a concave portion of the pile driving cap. After driving the small diameter portion into the ground and driving the small diameter portion to a predetermined depth, the cap for pile driving is removed and a large diameter portion is connected to a pile head of the small diameter portion via a predetermined connection portion. And driving the large-diameter portion into the ground using the driving surface in a state where the pile head of the large-diameter portion is fitted on the near side of the step formed in the pile driving cap. Construction method of piles on the ground. 2. A pile driving cap in which a recess into which a pile head is fitted is formed on one side and a driving surface is formed on the other side, wherein a step is formed on the inner surface of the recess, and the step is formed just before the step. The side is a large diameter recess for fitting the pile head of the large diameter part,
A pile driving cap, wherein a deeper side of the step is formed as a small diameter recess for fitting a pile head of a small diameter portion.