JPH0547685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a foundation pile structure that supports above-ground structures.

[Conventional technology and issues to be solved] Conventionally, multiple ready-made concrete piles or steel pipe piles are connected and driven to a predetermined depth in the ground below the structure as foundation piles, and the upper structure is There is a method of creating foundation piles to support it.

When designing and constructing such foundation piles, the load of the superstructure and the horizontal force acting on the structure are generally considered, and a pile suitable for the ground is selected and used. On the construction site,
Piles of the same type are connected together, and in particular, different types of piles with different pile performance in the length direction of the piles are connected.
No foundation piles were constructed at all.

For example, the following cylindrical piles are ready-made piles that cannot be expected to have a large circumferential bearing capacity when actually driven into the ground, but have a large horizontal bearing capacity: - Cylindrical prestressed concrete piles;
High-strength prestressed concrete piles (PC piles, PHC piles) ・ Composite piles (steel pipe concrete composite piles) ・ Steel pipe piles In addition, although the horizontal bearing capacity cannot be expected very much, knotted piles are used as ready-made piles with excellent peripheral bearing capacity. There are friction piles such as concrete piles, but as mentioned above, piles with different performance are connected and driven appropriately according to the characteristics of the ground to form foundation piles that support structures. Ta.

In particular, in addition to axial force and bending moment, a foundation pile actually driven into the ground is subject to negative frictional force depending on the ground, and there is also a risk of liquefaction in the ground during an earthquake. Therefore, it is desirable to build foundation piles that are optimal and most economical for each type of ground, but the conventional method of connecting and driving certain types of piles It is completely impossible to build a.

For example, in the ground shown in Fig. 12, the upper layer A of the ground is a soft, viscous, consolidated ground, and the lower layer B is a ground with a large N value and can be expected to have sufficient circumferential bearing capacity and tip bearing capacity for piles. horizontal force acting on the pile,
Assume that the bending moment is large.

In such a ground, if a cylindrical pile P such as a PHC pile or a steel pipe pile with a large horizontal bearing capacity is used for the entire length of the pile as shown in the figure, taking into consideration the bending moment, etc., the circumferential surface of the lower layer B ground will be Supporting capacity will be insufficient.

Furthermore, if the vertical bearing capacity of the above-mentioned ground is taken into account, and if a foundation pile is made of a knotted concrete pile with a large circumferential bearing capacity for the entire length of the pile, the horizontal bearing capacity of the upper layer A of the ground will be insufficient. Furthermore, since the circumferential surface bearing capacity is large, when the upper layer A of the ground consolidates and settles, a negative frictional force acts on the upper part of the pile body, and as a result, in addition to the axial force due to the structure load, the pile body It also takes a lot of energy.

Therefore, conventionally, foundation piles have been constructed using extremely uneconomical methods such as increasing the diameter of the same type of pile, increasing the length of the pile, or increasing the number of piles.

In view of the above, the present invention has been made to create a safe and economical foundation pile that has a bearing capacity that is compatible with the properties of the ground.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention installs cylindrical prestressed concrete piles, steel pipe piles, etc. with high bending strength in the upper ground where relatively large horizontal strength is required. Instead of using cylindrical piles, we decided to use knotted concrete piles with excellent circumferential bearing capacity in the subsoil where vertical bearing capacity such as circumferential bearing capacity can be expected, without increasing the pile diameter particularly in the lower part. Also, it is possible to improve the horizontal strength.

That is, the foundation pile structure of the present invention includes a ready-made cylindrical pile at the top of the foundation pile that supports the horizontal load acting on the structure, and a ready-made cylindrical pile below this which has a joint having approximately the same diameter as the diameter of the cylindrical pile. It is characterized by the construction of knotted concrete piles, and these two piles are connected and cast into the ground.

In the above, the ready-made cylindrical pile on the upper part of the foundation pile is a perforated pile having permeable holes that communicate with the inside and outside of the pile, and sand, gravel,
It is desirable to fill it with a filler such as crushed stone.

[Function] According to the foundation pile of the present invention having the above configuration,
Cylindrical piles with high bending strength are used in the upper ground where a relatively large bending moment acts, so the horizontal loads acting on the superstructure can be sufficiently supported by the cylindrical piles.
In addition, this cylindrical pile has a smaller circumferential frictional support force than that of a knotted concrete pile, so even if the upper layer is soft and viscous and may undergo consolidation settlement, no negative frictional force will occur. .

In addition, knotted concrete piles with high circumferential bearing capacity are used in the sub-soil, so
Even if the diameter of the trunk is smaller than the cylindrical pile, the knots have approximately the same diameter as the cylindrical pile and have sufficient tip support, and this, together with the increase in circumferential support due to the knots, Sufficient vertical support force can be obtained without any shortage.

In particular, although the pile diameter of a knotted concrete pile is smaller than the diameter of the upper cylindrical pile, it has knots that are approximately the same diameter as the cylindrical pile, so it is not a simple cylindrical pile. The horizontal bearing capacity is larger than that of the foundation pile, and the horizontal force is transmitted smoothly between the upper cylindrical pile and the lower jointed concrete pile without any large step, and the foundation pile as a whole can maintain a large horizontal bearing capacity. .

Furthermore, if the cylindrical pile is made into a perforated pile and its inner and outer peripheries are filled with filler such as sand, gravel, crushed stone, etc., the horizontal bearing capacity increases, and
The inner and outer fillers, such as gravel and crushed stone, have water permeability, and the inside and outside of the pile are connected through permeable holes, so the inner and outer holes of the pile serve as passageways for pore water to escape during an earthquake. It can drain excess pore water and effectively dissipate excess pore water pressure.

[Example] Next, an example of the present invention will be specifically described based on the drawings.

In the figure, P indicates a ready-made cylindrical pile used in the upper ground, F indicates a ready-made knotted concrete pile (hereinafter referred to as a knotted pile) used below the cylindrical pile, and these cylindrical piles P and knotted The required number of piles F are connected according to the ground properties, required pile bearing capacity, etc.
As illustrated in FIGS. 1 and 5, the foundation piles are driven into the ground to create foundation piles.

The cylindrical pile P and the knotted pile F are connected, for example, as shown in FIG. 2, when the diameter of the body 3 of the knotted pile F and the diameter of the cylindrical pile P are the same. As shown in FIG. 3, an end fitting 4 consisting of an end plate 4a and a side plate 4b is fixed to the ends of the cylindrical pile P and the knotted pile F that are connected in this way. The ends of the main reinforcing bars 5 inside are engaged. The piles P, F are connected by welding the end fittings 4, 4 together.

Figure 4 shows a case where reinforcing bars 5a are provided inside the pile cap at the top of the knotted pile F, separate from the main pile reinforcement, in order to increase the bending strength at the joints of the knotted pile F. . This is particularly effective when the bending strength of the upper and lower piles differs greatly by using the knotted pile F whose trunk diameter is smaller than that of the cylindrical pile P as in the present invention.

In the present invention, the diameter of the trunk 3 of the knotted pile F used in the lower part is not the same as that of the upper cylindrical pile P as described above, but as shown in FIGS. 5 and 6. In this method, a knotted pile F having knots 2 having approximately the same diameter as the diameter of the cylindrical pile P, that is, a pile whose body part 2 has a smaller diameter than the cylindrical pile P is used, and this knotted pile F is connected to the cylindrical pile P. It is then poured into the ground.

In this case, the upper and lower cylindrical piles P and knotted piles F are connected to the tapered joint pipe T as shown in the figure.
As this joint pipe T, a tapered pipe whose upper part has the same diameter as the diameter of the cylindrical pile P and whose lower part has the same diameter as the body part 3 of the joint pile F is used. In particular, a pipe whose wall thickness is comparable to or larger than the bending strength of the cylindrical pile P is used.

By doing this, the diameter of the cylindrical pile P that becomes the upper part of the foundation pile is larger than the diameter of the body 3 of the knotted pile F, so that the bending strength increases and the axial compressive strength also increases.

In the above embodiment, as the cylindrical pile P connected to the upper part, in addition to cylindrical concrete piles (PC piles, PHC piles, etc.), composite piles (steel pipe concrete composite piles), steel pipe piles 6, etc. can be used. Each type is used appropriately depending on the vertical bearing capacity, horizontal bearing capacity, soil properties, construction method, etc. of the piles that support the structure.

In addition, since the bending moment mainly acts on the upper part of the pile near the ground on the foundation pile, the cylindrical pile P at the upper part of the pile to be connected as described above should be a pile with a higher bending strength than the knotted pile F. This is desirable.

Furthermore, when using, for example, a steel pipe pile 6 as the cylindrical pile P, a ribbed steel pipe pile (not shown) with striped ribs provided on the inner and outer surfaces of the steel pipe may be used, or a As illustrated in FIG. 7, a perforated steel pipe pile 6 in which a plurality of permeable holes 7 are provided in the wall surface of the steel pipe can be used. The perforated pile 6 provided with permeable holes 7 is particularly effective as a foundation pile for preventing the ground from liquefying in the event of an earthquake when the upper ground is sandy ground, as will be described later.

In addition, in FIG. 7, the body 3 of the knotted pile F has approximately the same diameter as the cylindrical pile P, but when carrying out the present invention, the knot 2 of the knotted pile F is connected to the cylindrical pile P.
It will be made to have approximately the same diameter.

In addition, the pile length to be driven is long, multiple piles,
For example, when four piles are installed in a connected manner, only the top one is made into a cylindrical pile P, the three below it are made into a knotted pile F, or the top two piles are made into a cylindrical pile P. The lower two piles can be made of knotted piles F, or the upper three can be made of cylindrical piles P, and only the lowest part can be made of knotted piles F. Use the appropriate one depending on the ground, horizontal bearing capacity, vertical bearing capacity R, etc. Bye.

A method for constructing and constructing the foundation pile of the present invention in the ground using the above-mentioned connection structure will be explained below.

First, in order to carry out the driving method, as shown in FIG. 8, a knotted pile F is built on a predetermined ground, and then hammered with a diesel hammer 10 or the like and driven into the ground. In this case, as the knotted pile F penetrates, gravel 11 or the like is filled from the circumference of the pile (see figure a).
If the length of the knotted pile to be installed is long, add another knotted pile F1 and drive in the same way.

Next, the cylindrical pile P is added to the end fitting 4 by welding or other means, but at this time, gravel 11, sand, etc. Fill it with the filler material [Figure b]. Moreover, after driving a predetermined length, the upper part of the inner hole of the pile, such as the cylindrical pile P, may be filled with sand, gravel, etc., for the purpose of increasing the horizontal strength of the pile.

In addition, when gravel, crushed stone, etc. are filled as a filler, the drainage effect of the filled gravel becomes effective in dissipating excess pore water pressure during an earthquake. When using a steel pipe pile 6 or the like with empty holes provided, the filled portions of gravel, etc. inside and outside the pile are communicated through the permeable holes 7, so the drain effect of the filled gravel, etc. is further increased,
It is effective in dissipating excess pore water pressure during earthquakes and is effective in preventing ground liquefaction.

If the cylindrical pile P portion is long, additional cylindrical piles P may be added and driven in the same manner as described above.

As described above, foundation piles are constructed underground using cylindrical piles P in the upper ground and knotted piles F in the ground below [Figure c].

To install the above foundation pile using a low-noise pre-drilling method such as the cement milk method, proceed as follows.

As shown in Figure 9a, the screw auger 1
A hole with a diameter slightly larger than the diameter of the knot 2 of the knotted pile F is dug into the ground to a predetermined depth. When pulling up this screw auger 12,
is filled with a hardening liquid M such as cement milk or mortar.

This hardening liquid M, such as milk, has a high strength around the knotted pile F and the tip hardening part [M1 part in Fig. 10], and a low strength liquid around the cylindrical pile P [the same (Fig. M2 part) It is also possible to change the composition in the depth direction of the pile, such as by filling it. It is desirable to use a filling liquid that can provide high strength in areas where vertical bearing capacity of the pile is expected.

In this way, the knotted pile F is suspended and press-fitted into the borehole K. At this time, a predetermined number of knotted piles F are added. Next, the cylindrical pile P is added and press-fitted into the hole K by suspending it in the same manner as above.

As a result, foundation piles using cylindrical piles P in the upper ground and knotted piles F in the ground below are constructed underground.

The periphery of the cylindrical pile P may be filled with sand 13, gravel 11, etc. instead of the hardening liquid M such as cement milk (FIGS. 7 and 11).
In this case, gravel 11 or the like may be dropped into the gap from around the pile on the ground to fill it. Further, after the cylindrical pile P is sunk and press-fitted, a casing may be separately hung into the gap around the pile, and gravel or the like may be filled while compacting with the casing. In this case, it is also effective in increasing the horizontal bearing capacity.

Furthermore, when the cylindrical pile F at the top of the pile is a steel pipe pile 6 or the like, not only the outer periphery of the pile but also the inner hole of the pile may be filled with gravel, as in the case of the driving method described above.

In addition to the method described above, the foundation pile of the present invention can also be produced by a mixing method in which a ready-made pile is press-fitted into a cement soil excavation hole in which earth and sand in the ground and injection hardening liquid are mixed. The method in this case is almost the same as the pre-drilling method.

In addition, Fig. 8~ in the explanation of the above-mentioned land preparation work
In FIG. 11, for convenience, the body 3 of the knotted pile F is
Although the diameter of the lower knotted pile F is shown to be approximately the same diameter as the cylindrical pile P, when carrying out the present invention, the diameter of the knot portion 2 of the lower knotted pile F is of course approximately the same diameter as the cylindrical pile P. Become.

In the foundation pile of the present invention constructed as described above, in the upper ground, concrete piles with a large amount of prestress such as PC piles and PHC piles, in particular, are used as cylindrical piles P with a large bending capacity.
Alternatively, composite piles (steel pipe concrete composite piles) or steel pipe piles 6 with high bending capacity are selected and used as appropriate depending on the axial force acting on the foundation pile, the magnitude of the bending moment, and the ground properties. P can sufficiently support the horizontal load acting on the superstructure.

In addition, in the lower ground, knotted piles F are used that can be expected to have a large circumferential bearing capacity R due to the presence of knots 2, so it is possible to obtain sufficient vertical bearing capacity without any shortage, and this allows the upper part to It can compensate for the lack of vertical support capacity. Therefore, it is possible to obtain a safe, strong, and economical foundation pile that has a bearing capacity that is compatible with the soil.

In particular, the tip of the knotted pile F is usually embedded in the support layer, but even if the diameter of the trunk 3 is smaller than the cylindrical pile P, the knot 2 has approximately the same diameter as the cylindrical pile P. It has sufficient tip bearing capacity, making it a more economical and safe foundation pile.

Furthermore, although the pile diameter of the knotted pile F is smaller than the diameter of the upper cylindrical pile P, since the knot 2 has approximately the same diameter as the diameter of the cylindrical pile P, it has a simple cylindrical shape. The horizontal force is larger than the pile, and the horizontal force is transmitted smoothly between the cylindrical pile P at the top and the knotted pile F at the bottom, resulting in a smooth transmission of horizontal force. can.

In addition, in soft and viscous ground, when the upper layer of the ground consolidates and settles, a negative frictional force acts on the upper part of the pile body, so if the circumferential bearing capacity is large, the pile body will be affected by the above negative frictional force in addition to the axial force due to the structure load. Axial force will also be borne, but according to the above-mentioned foundation pile of the present invention, cylindrical piles with small circumferential bearing capacity are used in the upper ground, so axial force due to negative frictional force is borne. Never.

In addition, when implementing the foundation pile of the present invention using the pre-drilling method, the strength of the hardening liquid such as cement milk that is injected into the hole is changed, and a high-strength hardening liquid is injected into the lower ground, and the hardening liquid is injected into the upper ground. If a hardening liquid with low strength is injected, the negative frictional force applied to the cylindrical pile will be reduced, and safe foundation piles can be constructed more economically, in the same way as described above.

[Effect of the invention] As described above, according to the foundation pile structure of the present invention,
By connecting and placing cylindrical piles with high bending capacity in the upper ground, which requires relatively large horizontal bearing capacity, and knotted concrete piles with excellent circumferential bearing capacity in the lower ground, the upper ground It is possible to construct safe foundation piles with excellent horizontal bearing capacity in the ground and vertical bearing capacity in the underlying ground. In addition, in cases where the upper layer is soft and viscous, even if the upper layer is consolidated and settles, the upper layer is made of cylindrical piles with a small circumferential bearing capacity, so the negative frictional force There is no need to bear the burden of axial force. Therefore, in combination with the horizontal bearing capacity of the upper part of the pile and the vertical bearing capacity of the lower part, it is particularly suitable for use in soft and viscous ground.

In particular, in the case of the present invention, although the pile diameter of the knotted concrete pile is smaller than the diameter of the upper cylindrical pile, it has knots that are approximately the same diameter as the diameter of the cylindrical pile. The horizontal strength is higher than that of a simple cylindrical pile, and the horizontal force is transmitted smoothly between the upper cylindrical pile and the lower knotted concrete pile without creating a large step, so the foundation pile as a whole has a higher Since it is possible to maintain a large horizontal bearing capacity, it is possible to economically construct a safe foundation pile with a bearing capacity suitable for the ground without increasing the diameter of the knotted pile.

Furthermore, if the cylindrical pile is made into a perforated pile and the inner and outer peripheries of the cylindrical pile are filled with filler such as sand, gravel, crushed stone, etc., the resulting compaction not only increases the horizontal bearing capacity of the surrounding ground, but also If the filling material is gravel, crushed stone, etc., the drain effect will effectively dissipate excess pore water pressure during an earthquake, and it will be possible to construct strong foundation piles that are also effective in preventing ground liquefaction.

[Brief explanation of the drawing]

Fig. 1 is a schematic front view illustrating a foundation pile structure in which a cylindrical pile and a knotted concrete pile are connected, Fig. 2 is a partially enlarged front view of the same as above, Fig. 3 is a partial sectional view of the end of the pile, Fig. 4 is a partial front view showing another example of the same as above, Fig. 5 is a partial front view showing an embodiment of the foundation pile structure of the present invention, Fig. 6 is a partially enlarged front view of the same as the above, and Fig. 7 is still another example. Figures 8a, b, and c are schematic cross-sectional views illustrating the construction state of the foundation pile structure of the present invention, and Figures 9a, b, and c are partial cross-sectional views showing examples of the foundation pile structure of the present invention. 10 is a partially enlarged view of the same as above, FIG. 11 is a partially enlarged sectional view of another example, and FIG. 12 is an explanatory view of a conventional example. P...Cylindrical pile, F...Knotted concrete pile, 2...Knot, 3...Body, 4...End fitting, 5...Main reinforcement, 5a...Auxiliary reinforcement, 6...Steel pipe pile, 7...Water hole, 11...Gravel, 13...
Sand, M... hardening liquid.

Claims (1)

[Scope of Claims] 1. A ready-made cylindrical pile is installed at the upper part of the foundation pile that supports the horizontal load acting on the structure, and a ready-made knotted pile having a knot approximately the same diameter as the diameter of the cylindrical pile is installed below this pile. A foundation pile structure characterized by arranging concrete piles, connecting both piles and driving them into the ground. 2. The ready-made cylindrical pile at the top of the foundation pile is a perforated pile with permeable holes that communicate with the inside and outside of the pile,
The foundation pile structure according to claim 1, wherein the inner and outer peripheries of the cylindrical pile are filled with filler such as sand, gravel, crushed stone, etc.