JP7567718B2 - Pile installation method and method for calculating supply amount of lubricant used in said pile installation method - Google Patents

Description

The present invention relates to a method for constructing a pile by rotating a tubular pile into the ground, and a method for calculating the amount of lubricant to be supplied for use in the pile construction method.

Many methods have been proposed for driving a tubular pile, such as a steel pipe pile, into the ground by rotating the pile.
For example, Patent Document 1 discloses a method for constructing a row of steel pipe piles by driving cutting steel pipe piles with a bit at the tip into a concrete revetment using a steel pipe pile driving device that rotates and drives the steel pipe piles in. The use of cutting steel pipe piles with a bit at the tip has the advantage of increasing cutting ability and being able to destroy existing structures such as concrete and obstacles.

In the construction of tubular piles, particularly in the method of rotary driving of existing piles, in order to obtain the bearing capacity of the pile, after punching through existing structures such as concrete, rotary driving of the pile is continued to a specified depth in the ground (e.g., the supporting layer). During this process, the soil of the excavated ground, rocks of the ground destroyed during excavation, or fragments of structures destroyed during excavation (hereinafter collectively referred to as "soil") create voids, reducing the bulk density and expanding the apparent volume. Therefore, the soil inside the pile and the soil on the outer periphery of the pile restrain the tubular pile from the inside and outside, respectively, and become a resistance when it is pressed into the pile.
In addition, the increase in the force of the soil trapped in the pile that restrains the tubular pile leads to an increase in the friction between the inner surface of the pile and the soil inside the pile. Therefore, as the amount of excavated soil trapped in the pile increases, the phenomenon of soil clogging occurs inside the pile. The clogging inside the pile by the excavated soil further increases the pressing resistance of the tubular pile during construction.

Therefore, an auxiliary construction method for preventing blockage inside the pile during construction and reducing press-in resistance is disclosed, for example, in Patent Document 2. In Patent Document 2, a fluid such as water is discharged in the circumferential direction along the inner wall of the steel pipe pile near the tip of the steel pipe pile. As a result, the fluid is interposed between the inner wall of the steel pipe pile and the soil inside the pile, reducing friction between the inner wall of the pile and the soil inside the pile, making it difficult for the excavated soil to block the pile.
Another method is to use a screw auger placed inside the steel pipe pile to lift up and remove the soil inside the pipe, thereby preventing the inside of the pile from becoming clogged with soil and sand.

JP 4105076 A JP 4242251 A

As mentioned above, in the construction of tubular piles, it is necessary to prevent blockage of the pile by soil and sand that occurs during the excavation process.
However, in the method of Patent Document 2, the soil inside the pile turns into mud when it mixes with the large amount of water discharged into the pile, and the muddy soil flows under the pile and is discharged to the ground from the outer surface of the pile, resulting in increased costs and environmental problems due to the disposal of the discharged soil (discharged soil).
The same problem occurs when using a screw auger in combination with other construction methods, as soil is discharged from inside the pile.

Furthermore, it is difficult to control the scope of application of these auxiliary methods, and in actual construction, they are often applied in excess of the necessary scope to prevent areas from not being covered. In this case, although workability is improved, the ground at the specified depth reached by the pile tip will be loosened or disturbed. In particular, when it is desired to obtain high bearing capacity by burying the tip of the pile in the supporting layer, loosening the supporting layer leads to a decrease in the bearing capacity of the pile, which is a very serious problem. Therefore, it is necessary to take separate measures to ensure that the pile exerts its bearing capacity, such as constructing a base reinforcement section with cement mortar at the tip of the pile, which makes construction more complicated.

The present invention has been made to solve these problems, and aims to provide a pile construction method that can prevent blockage of the pile due to soil and sand without loosening or disturbing the ground at a specified depth and also suppress the occurrence of soil removal, as well as a method for calculating the supply amount of lubricant used in the pile construction method.

(1) The pile construction method of the present invention is a method for rotary-inserting a tubular pile into the ground, and when rotary-inserting the pile, a lubricant that is statically more viscous than water and has shear-thinning properties, that is, its viscosity decreases when subjected to shear, is supplied between the inner wall of the pile and the soil and sand inside the pile.

(2) In addition, in the above (1), the lubricant is supplied from the lubricant stored inside the pile.

(3) In addition, in the above-mentioned (1) or (2), the lubricant is not supplied after the pile reaches a predetermined depth in the ground.

(4) In the device described in (1) or (2) above, the supply amount V(L) of the lubricant is set so as to satisfy the following formula (1):
19.4・π・D _in・(H-10D _out )≦V≦19.4・π・D _in・(H+5D _out ) ... (1)
Where, H: Distance from the ground surface to a given depth (m)
D _out : Outer diameter of pile (m)
D _in : Inner diameter of pile (m)

(5) A method for calculating a supply amount of a lubricant according to the present invention is a method for calculating a supply amount of a lubricant used in the pile construction method according to any one of (1) to (3) above,
Test construction is carried out on ground with similar properties to the target construction site.
determining a relationship between the application depth in the trial application and the amount of lubricant used;
The method includes a step of setting the amount of lubricant to be supplied based on the obtained relational expression, the inner circumference of the pile used in the trial construction, the actual construction depth, and the inner circumference of the pile to be used in the actual construction.

In the present invention, by rotating and penetrating the pile using a lubricant having shear thinning properties, which is statically more viscous than water and whose viscosity decreases when subjected to shear, the lubricant reduces friction between the inner wall of the pile and the soil inside the pile, thereby preventing blockage by the soil. In addition, in areas not affected by the shear force caused by the rotation of the pile, the lubricant does not penetrate into the soil inside the pile, preventing the ground around the pile from being loosened or disturbed more than necessary.
Therefore, it is possible to suppress the generation of muddy soil and sand as soil discharge. Also, the bearing capacity of the pile can be exhibited without additional construction such as the construction of a foot protection section.

FIG. 1 is a diagram for explaining a pile construction method according to the first embodiment of the present invention (part 1). FIG. 2 is an explanatory diagram of a pile construction method according to the first embodiment of the present invention (part 2). 2A and 2B are diagrams showing another embodiment 1 of the excavation member of the pile shown in FIG. 1, in which FIG. 2A is a cross-sectional view and FIG. 2B is a bottom view. 3A and 3B are diagrams showing another embodiment 2 of the excavation member of the pile shown in FIG. 1, in which FIG. 3A is a cross-sectional view and FIG. 3B is a bottom view. 4A and 4B are diagrams showing another embodiment 3 of the excavation member of the pile shown in FIG. 1, in which FIG. 4A is a cross-sectional view and FIG. 4B is a bottom view. FIG. 4 is a three-dimensional view showing another embodiment 4 of the excavation member of the pile shown in FIG. 1 . FIG. 5 is a three-dimensional view showing another embodiment 5 of the excavation member of the pile shown in FIG. 1 . FIG. 2 is a diagram illustrating a method for mixing lubricant materials. 10A to 10C are diagrams illustrating another aspect of the pile construction method according to the first embodiment of the present invention. 1 is a graph showing the relationship between the penetration length of a pile into the ground and the amount of lubricant used. 1 is a graph showing experimental results according to an embodiment, comparing an example of the invention (with lubricant) with a comparative example (without lubricant) from three perspectives.

[First embodiment]
The pile construction method according to this embodiment involves rotating a tubular pile into the ground to a predetermined depth, and during the rotational penetration, a lubricant that is statically more viscous than water and has shear thinning properties that reduce the viscosity when subjected to shear is supplied between the inner wall of the pile and the soil inside the pile. In this embodiment, the lubricant is supplied from a lubricant stored inside the pile.
Here, the tubular pile refers to a hollow cylindrical pile that is long in the axial direction. For example, a "precast pile" can be mentioned. More specifically, a prestressed concrete pile (PC pile), a pretensioned prestressed concrete pile (PHC pile), a SC pile with a steel pipe wrapped around the outer periphery of the concrete, a PRC pile made of concrete with high-strength reinforcing bars, or a steel pipe pile can be mentioned. Since the ratio of the pipe thickness to the pipe diameter (diameter-thickness ratio) is small and the penetration resistance is small, the application to a steel pipe pile is particularly preferable.
The predetermined depth is not particularly limited, but may be, for example, a depth to which the tip of the pile is to be designed. More specifically, it may be the penetration length, the vicinity of the supporting layer of the ground, or the top end of the supporting layer. The latter two correspond to the case where the tip of the pile is to be made to reach the supporting layer of the ground, and it is possible to increase the bearing capacity of the tubular pile.

As described above, the lubricant of the present embodiment has shear thinning properties, and has a viscosity that does not allow the lubricant to penetrate into the ground in a stationary state. The properties of the lubricant will be described in detail later.
Although the present invention is not limited to the method of supplying the lubricant between the inner wall of the tubular pile and the soil inside the tubular pile, a method of simply supplying the lubricant includes a method of storing the lubricant inside the pile, particularly on the soil in the ground, and applying the lubricant thereto. This method will be specifically described below as an example.

2(a), with the bottom end of the pile 1 driven into the ground 3, lubricant 5 is poured into the pile from the top end side of the pile 1, and a predetermined amount of lubricant 5 is accumulated inside the pile 1. Due to the characteristics described below, the lubricant 5 naturally accumulates on top of the soil of the ground 3 (on the surface of the ground 3 in this figure).
Next, as shown in FIG. 2( b ), the pile driver 7 has a leader 9 which grips the upper end of the pile 1 and rotates to drive the pile 1 into the ground 3 .
By doing as described above, the pile 1 can be constructed by the rotary penetration method while supplying the lubricant 5 stored in the pile 1 between the inner wall of the pile 1 and the soil inside the pile 1. This will be described in detail with reference to FIG.

Fig. 1 shows the state in which the pile 1 is rotated and driven into the ground 3 with the lubricant 5 stored inside the pile 1, Fig. 1(a) is a plan view, and Fig. 1(b) is a vertical cross-sectional view. The lubricant 5 used in the present invention has a static viscosity higher than that of water. Therefore, even if the lubricant 5 is poured into the pile 1 and comes into contact with the surface of the ground 3, it does not permeate into the ground 3 like water does, but is retained on top of the soil and sand of the ground 3 and accumulates inside the pile 1.
When the pile 1 is rotated and inserted in this state, the lubricant 5 near the inner wall of the pile 1 is subjected to a shear force as shown by the white arrow in Figure 1(a) and its viscosity decreases (see the light gray area in Figure 1(a)).
1(b), the lubricant 5 permeates like water into the soil of the ground 3 along the inner wall of the pile 1, and is supplied between the inner wall of the pile 1 and the soil inside the pile 1. In other words, the lubricant 5 is supplied by lowering the viscosity of the lubricant 5 stored inside the pile 1 by shearing caused by the rotation of the pile 1, and as a result, the lubricant 5 permeates into the soil of the ground 3 along the inner wall of the pile 1. This reduces friction between the inner wall of the pile 1 and the soil inside the pile 1, improving workability and preventing soil blockage inside the pile 1.
1(a) and (b), the lubricant 5 in the area away from the inner wall of the pile 1 (see the dark gray area in FIG. 1) remains static and has a higher viscosity than water, so it does not penetrate into the soil of the ground 3 and is held on top of the soil of the ground 3, remaining pooled within the pile 1. As the rotational penetration progresses, a portion of the lubricant 5 that remains pooled within the pile 1 is newly supplied between the newly generated inner wall of the pile 1 and the soil within the pile 1.

In this embodiment, the pile 1 is provided at its tip with an excavation member 11 that is provided so as to protrude inward of the pile 1. This excavation member 11 is preferable because it temporarily forms a gap between the inner wall of the pile 1 and the soil inside the pile 1 when the pile 1 is rotated and inserted, making it easier for the lubricant 5 to penetrate and allowing for effective supply.

As another embodiment of the excavation member 11, for example, as shown in FIG. 3, a tubular member having a thickness greater than the thickness of the pile 1 may be provided at the tip of the pile 1 (another embodiment 1). As shown in FIG. 4, a bit having a width greater than the thickness of the pile 1 may be provided at the tip of the pile 1 (another embodiment 2).

Furthermore, as shown in Fig. 5, the bit may be provided on the inner wall of the pile 1 (Other embodiment 3). It is empirically known that soil blockage in the pile 1 occurs above a height of more than _Din ( _Din : inner diameter of the pile) from the tip side. For this reason, in the case of Other embodiment 3, it is preferable that the bit is provided at a height within _Din from the tip of the pile.
Also, as shown in Figs. 6 and 7, a spiral blade or a double spiral blade may be provided so as to protrude inward from the pile 1 (other embodiment 4, other embodiment 5).

As described above, the excavation members 11 that form gaps on the inner peripheral surface of the pile 1 may be arranged continuously or discretely in the circumferential direction.
Moreover, the gap formed on the inner peripheral surface of the pile 1 can be a very small space because it is for the purpose of facilitating the supply of the lubricant 5 between the inner wall of the pile 1 and the soil inside the pile 1. Therefore, it is sufficient for the width of the excavation members 11 to protrude inward from the pile 1 to be 5 mm or more.
It should be noted that the excavation members 11 that form gaps on the inner peripheral surface of the pile 1 are not essential, and an ordinary pipe that does not have these excavation members 11 may be used as the pile.

Next, the lubricant 5 of this embodiment will be described in detail below.
As described above, the lubricant 5 in this embodiment has a static viscosity higher than that of water, and has shear thinning properties, that is, the viscosity decreases when the lubricant is subjected to shear. Examples of the lubricant 5 include bentonite liquid and liquids containing water-soluble polymers.

As described above, the lubricant 5 of this embodiment has a static viscosity higher than water. Such lubricant 5 is less likely to penetrate than water into the soil inside the pile 1 or into the ground 3 at a specified depth reached by the tip of the pile 1 unless a shear force is applied. Therefore, compared to the conventional method of construction in which water is discharged onto the inner wall of the pile 1, loosening or disturbing the ground 3 can be suppressed. As a result, the bearing capacity of the pile 1 can be exhibited. In addition, since the soil inside the pile 1 is not turned into mud, the occurrence of soil removal can also be suppressed.

It is also preferable to adjust the viscosity of the lubricant 5 according to the permeability of the ground 3 to be excavated. This point will be explained below.

k：潤滑剤の透水係数(m/s)、ρ：潤滑剤の密度(g/cm³)、μ：潤滑剤の粘性係数(Pa・s)
k_w：水の透水係数(m/s)、ρ_w：水の密度(g/cm³)、μ_w：水の粘性係数(Pa・s)
なお、上記のμは、「液体の粘度測定方法（JIS Z 8803、2011）」で測定した、ずり速度0.01(1/s)以下における潤滑剤５の粘性係数とする。また、上記のk_wは、「土の透水試験方法」で測定した、地盤３のうち最も粒度が粗い層における水の透水係数とする。ρ_w、μ_wは、「土の透水試験方法」に記載の水の密度、粘性係数とする。 Generally, the permeability coefficient, which indicates the permeability of the ground 3, can be obtained by the "Soil Permeability Testing Method" (JIS A 1218, 2009). The "Soil Permeability Testing Method" is based on the permeability of water at a temperature of 15 degrees Celsius. It is known that at the same temperature, the permeability is proportional to the density of the liquid and inversely proportional to the viscosity coefficient. Therefore, by taking into account the density and viscosity of the lubricant 5 at a temperature of 15 degrees Celsius and making corrections, the permeability coefficient of the lubricant 5 in the ground 3 is defined by the following formula (2).

k: Permeability coefficient of lubricant (m/s), ρ: Density of lubricant (g/cm ³ ), μ: Viscosity coefficient of lubricant (Pa·s)
k _w : Permeability coefficient of water (m/s), ρ _w : Density of water (g/cm ³ ), μ _w : Viscosity coefficient of water (Pa·s)
The above μ is the viscosity coefficient of the lubricant 5 at a shear rate of 0.01 (1/s) or less, measured by the "Method of measuring viscosity of liquids (JIS Z 8803, 2011)." The above _kw is the permeability coefficient of water in the coarsest layer of the ground 3, measured by the "Method of testing permeability of soil. _{" ρw} and _μw are the density and viscosity coefficient of water described in the "Method of testing permeability of soil."

In the present invention, "statically more viscous than water" means that the permeability coefficient k of the lubricant 5 at a temperature of 15 degrees Celsius calculated by the above formula (2) is smaller than the permeability coefficient _kw of water at a temperature of 15 degrees Celsius. Here, in the case of ground with a coarse grain size and uniform particle size, the permeability is generally high, and the permeability coefficient _kw of water according to the "soil permeability test method" can be 1× ^10-3 (m/s) or more. Therefore, it is preferable that the viscosity coefficient μ of the lubricant 5 is at least 100 times the viscosity coefficient _μw of water.
Specifically, if the viscosity of the lubricant 5 is set so that the permeability coefficient k of the above-mentioned lubricant 5 satisfies the following formula (3), it can be reliably determined that the lubricant 5 does not penetrate into the ground 3 when in a stationary state in the ground 3 where the pile 1 is constructed, which is preferable.
k＜1× ^10-5 ...(3)
If the lubricant 5 has a viscosity that does not allow it to penetrate into the ground 3 in a stationary state, the lubricant 5 will not penetrate anywhere other than between the inner wall of the pile 1 and the soil inside the pile 1. This makes it possible to minimize the amount of lubricant 5 used. Furthermore, it is also possible to store the lubricant inside the pile 1, particularly on top of the soil of the ground 3.

Also, since the lubricant 5 does not penetrate into the soil and sand inside the pile 1, the amount of lubricant 5 required for construction can be calculated in advance. Specific examples of the calculation method will be described later in the second and third embodiments, but the amount of lubricant 5 required for construction can be calculated based on the inner diameter and penetration length of the pile 1. Here, the penetration length of the pile 1 corresponds to the "predetermined specified depth." Also, when the tip of the pile is to reach the supporting layer of the ground 3, the "depth from the ground surface to the top of the supporting layer in the ground 3" is used instead of the "predetermined specified depth."

As described above, the lubricant 5 of the present embodiment has shear thinning properties, that is, the viscosity of the lubricant decreases due to shear force. A fluid having such properties is called a pseudoplastic fluid, and the higher the shear rate (=shear rate), the lower the viscosity of the fluid.
The lubricant 5 is preferably one having a large degree of viscosity reduction due to shear, since the lubricant 5 can easily penetrate between the soil and sand in the pile 1 and the inner wall of the pile 1. Specifically, it is preferable that the following formula (4) is satisfied.
(μ´/μ)＜1× ^10-1 ...(4)
μ: Viscosity coefficient of the lubricant at a temperature of 15 degrees Celsius and a shear rate of 0.01 (1/s) or less (Pa s)
μ´: Viscosity coefficient of the lubricant at a temperature of 15 degrees Celsius and a shear rate of 2.5 (1/s) or less (Pa s)
The viscosity coefficient of a liquid as a function of shear rate can be measured using a rotational viscometer as described in "Method of Measuring Viscosity of Liquids."

Examples of the lubricant 5 having the above-mentioned properties include a bentonite liquid obtained by mixing 120 kg or more of bentonite per 1 ^m3 of water, and a liquid obtained by mixing 3 kg or more of an acrylic acid-based water-soluble polymer per 1 ^m3 of water.

As a method for mixing the materials for the lubricant 5 as described above, for example, a dynamic mixer method or a static mixer method can be used.
In the dynamic mixer system, as shown in FIG. 8( a ), ingredients for lubricant 5 are placed in a water tank 13, mixed with a mixer 15 to produce lubricant 5, and the produced lubricant 5 is pumped by a pump 17.
In the static mixer method, as shown in FIG. 8( b ), the materials for the lubricant 5 are simultaneously fed into a pipe 19 and mixed while being fed by turbulent stirring generated by a mixing element 21 provided in the pipe 19.

The dynamic mixer method can mix any kind of raw material for the lubricant 5, but requires a separate water tank 13 and mixer 15 for mixing, which increases the size of the construction equipment.
In the static mixer method, the raw material of the lubricant 5 must be in a liquid state, but since the mixer 15 is not required, the equipment can be simplified.
Therefore, it is advisable to select an appropriate mixing method according to the material, for example, a dynamic mixer method when the material for the lubricant 5 contains powder, and a static mixer method when the material is all liquid.

1 and 2, an example is described in which the pile 1 is rotated and driven in a state in which the lubricant 5 is stored inside the pile 1, but the present invention is not limited to this. For example, the lubricant 5 may be stored in a storage tank (not shown) provided on the outside of the pile 1, and the lubricant 5 may be supplied from the storage tank into the pipe of the pile 1.
9, a lubricant supply pipe 23 for supplying the lubricant 5 may be disposed axially along the inner wall of the pile 1, and the lubricant 5 may be discharged from a discharge hole formed at the tip of the lubricant supply pipe 23 to supply the lubricant 5 between the inner wall of the pile 1 and the soil inside the pile 1. In this case, the discharge hole for discharging the lubricant 5 may be provided not only at the tip of the lubricant supply pipe 23 but also on the side surface.

As described above, in this embodiment, by supplying lubricant 5 having shear thinning properties between the inner wall of pile 1 and the soil inside pile 1 while rotating and penetrating pile 1, the lubricant 5 reduces friction between the inner wall of pile 1 and the soil inside pile 1, improving workability and suppressing soil blockage.
In addition, in areas not affected by the shear force caused by the rotation of the pile 1, the lubricant 5 has a higher viscosity than water and is therefore less likely to penetrate into the soil. This makes it possible to prevent the ground 3 around the pile 1 from being loosened or disturbed more than necessary, and also to prevent the muddy soil from being discharged onto the ground.
In particular, when constructing a tubular pile in soil (or ground containing it) with a coarse grain size and uniform particle size, the soil inside the pile has high permeability, and water penetrates into the soil without mixing with the sand. Therefore, even if water is used, the friction between the inner wall of the pile and the soil inside the pile is not reduced, and blockage inside the pile is likely to occur. Even in such soil conditions, the construction method of the present invention reduces the friction between the inner wall of the pile 1 and the soil inside the pile 1, improving workability and suppressing soil blockage. In other words, the construction method of the present invention can obtain the above effects regardless of the properties of the ground, that is, even in highly permeable ground, without any problems.

[Embodiment 2]
In the first embodiment, the lubricant 5 is supplied between the inner wall of the pile and the soil inside the pile, thereby reducing resistance during construction and preventing blockage of the pile with soil.
Although the lubricant 5 is less likely to penetrate into the soil and to loosen the ground 3 than the water that has been used conventionally, it is possible to actively cause soil blockage by controlling the supply of the lubricant 5 and not supplying the lubricant 5 at a certain depth. In this case, the bearing capacity of the pile 1 can be further improved.

One example of such control of the supply of the lubricant 5 is to control the timing of stopping the supply. Specifically, after the tip of the pile reaches a predetermined depth in the ground 3, the lubricant 5 is not supplied.
In the pile construction method of this embodiment, the pile 1 is rotated and penetrated into the ground 3 in a layer (middle layer) before the predetermined depth as described in the first embodiment while supplying the lubricant 5. After the tip of the pile 1 reaches the predetermined depth, the pile 1 is rotated and penetrated without supplying the lubricant 5. In particular, when the tip of the pile 1 is rotated and penetrated into the supporting layer, the above-mentioned "predetermined depth" may be replaced with "near the supporting layer". In this way, the tip of the pile 1 can reach the supporting layer without loosening or disturbing the supporting layer and while causing soil blockage.
In addition, in the case where the lubricant 5 is directly supplied to the vicinity of the tip of the pile 1 through the lubricant supply pipe 23 as shown in Fig. 9, the discharge of the lubricant 5 from the lubricant supply pipe 23 may be stopped when the tip of the pile 1 reaches a predetermined depth. Furthermore, in the case where the tip of the pile 1 is made to reach the supporting layer, the discharge of the lubricant 5 from the lubricant supply pipe 23 may be stopped when the tip of the pile 1 reaches the vicinity of the supporting layer.
As described above, according to this embodiment, by not supplying the lubricant 5 after the pile 1 reaches a predetermined depth, it is possible to actively cause soil blockage in the pile 1 at a predetermined depth in the ground 3 and improve the bearing capacity of the pile 1. Furthermore, when the tip of the pile 1 is allowed to reach the bearing layer, by not supplying the lubricant 5 after the pile 1 reaches the vicinity of the bearing layer, it is possible to actively cause soil blockage in the pile at the bearing layer and improve the bearing capacity of the pile 1.

[Embodiment 3]
Another example of controlling the supply of the lubricant 5 is to stop the supply by controlling the supply amount. Specifically, the lubricant 5 (for example, that stored in the pile 1 or in a storage tank) is exhausted when the tip of the pile reaches a predetermined depth in the ground 3. This method will be described in detail with reference to the case where the pile 1 is constructed by the method described in Figs. 1 and 2.
In the construction method of the piles in Figures 1 and 2, the pile 1 is rotated and inserted while a lubricant 5 is stored inside the pile 1, and the viscosity of part of the lubricant 5 is reduced by the shear force caused by the rotation of the pile 1. The reduced-viscosity lubricant 5 is then allowed to permeate the soil and sand of the ground 3, thereby supplying the lubricant 5 between the inner wall of the pile and the soil and sand inside the pile.
Therefore, the inventors conducted the following experiment to examine how much of the lubricant 5 stored inside the pile is supplied between the inner wall of the pile and the soil inside the pile.

In this experiment, a steel pipe with a diameter of 318.5 mm and a plate thickness of 7.9 mm was used as the pile 1, and after the tip of the steel pipe was driven into the ground 3, a certain amount of lubricant 5 was poured into the pile from above, and the steel pipe was rotated to penetrate (see Figure 2). At this time, the rotation was stopped at appropriate times to check the height of the lubricant 5 that had accumulated above the soil inside the pile. From this height, the amount of lubricant 5 remaining on the surface of the ground 3 was calculated, and the amount of lubricant 5 supplied was calculated from the difference with the initial amount poured in.
FIG. 10 shows the relationship between the penetration length of the steel pipe into the ground and the calculated supply amount of the lubricant 5.

As shown in FIG. 10, it is understood that the penetration length of the steel pipe and the supply amount of the lubricant 5 are in a proportional relationship.
As described above, the lubricant 5 has a static viscosity higher than that of water and a shear thinning property, that is, the viscosity of the lubricant 5 decreases when subjected to shear. Therefore, the amount of the lubricant 5 supplied per penetration length is considered to be proportional to the circumferential length of the inner diameter of the steel pipe.
From the above, the amount (L) of lubricant 5 required for 1 m of penetration can be expressed by the following formula (5): where D _in is the inside diameter of the pile (m), 18.433 is the proportionality coefficient in Figure 10, and 0.95096 is the circumference (m) of the inside diameter of a steel pipe with a diameter of 318.5 mm and a plate thickness of 7.9 mm.

The above formula (5) is the amount of lubricant 5 required for 1m of penetration, so by multiplying this by the penetration length (m) to be penetrated while rotating while supplying lubricant 5, the total amount of lubricant 5 required can be calculated, i.e., the amount of lubricant 5 that should be stored in the pile pipe before construction.

In addition, if the amount of stored lubricant 5 is the amount of penetration length X (m), the stored lubricant 5 will run out when the penetration length reaches X (m), and therefore no lubricant 5 will be supplied even if the pile 1 is rotated and penetrated to a depth beyond that.
Therefore, by setting the amount of lubricant 5 so that the lubricant 5 is used up when the pile 1 reaches a predetermined depth, it is possible to stop the supply of lubricant 5 after the pile 1 reaches the predetermined depth.
If the lubricant 5 is not supplied, as in the case of construction without using the auxiliary construction method, soil blockage occurs within the pile 1 as the pile 1 is rotated and penetrated, thereby improving the bearing capacity performance of the pile 1.
Furthermore, the above-mentioned "predetermined depth" refers to the "upper end of the supporting layer" when the tip of the pile is made to reach the supporting layer of the ground 3.

The case where the tip of the pile 1 reaches the supporting layer of the ground 3 will be further considered.
The depth to which the pile 1 is driven from the top of the supporting layer is generally set based on the outer diameter of the pile 1. For example, a support pile is generally driven from the top of the supporting layer to a depth of up to about 5 times the outer diameter of the pile. Therefore, when the lubricant 5 is supplied over the entire penetration length, the supply amount of the lubricant 5 may be up to about (H+5D _out ) times the amount shown in formula (5). Here, H is the depth (m) from the ground surface to the top of the supporting layer, D _out is the outer diameter (m) of the pile, and 5D _out is 5 times the outer diameter of the pile.

On the other hand, if it is desired to improve the bearing capacity of the pile 1 by not supplying the lubricant 5 to the bearing layer, it is preferable to set the supply amount so that the lubricant 5 is used up before the pile 1 reaches the bearing layer, as described above. How high up the lubricant 5 should be used up effectively depends on the ground conditions and the outer diameter of the pile 1, but it is preferable to use it up about 10 times the outer diameter of the pile 1, for example. Therefore, the supply amount of the lubricant 5 is at least (H- _10Dout ) times the amount shown in formula (5), where _10Dout is 10 times the outer diameter of the pile.
Therefore, when the tip of the pile is to reach the bearing layer of the ground 3 or into the bearing layer, it is preferable to set the supply amount V(L) of the lubricant 5 so as to satisfy the following formula (1).
19.4・π・D _in・(H-10D _out )≦V≦19.4・π・D _in・(H+5D _out ) ... (1)
This is the case where the tip of the pile 1 reaches the supporting layer, but the same effect can be obtained for other reasons. When the tip of the pile 1 does not reach the supporting layer, H may be set to "the distance from the ground surface to a predetermined depth in the ground 3". Here, if the "predetermined depth" is considered to be "up to the top of the supporting layer", the supply amount of the lubricant 5 can be controlled, including the case where the tip of the pile 1 reaches the supporting layer.

It should be noted that the above formula (1) is defined based on the proportionality coefficient (see FIG. 10) between the penetration length of the pile 1 and the amount of lubricant supplied, which was obtained from the above-mentioned experiment. However, it is also possible to carry out a similar experiment depending on the properties of the lubricant 5 and the ground 3, and set the amount of lubricant 5 supplied based on the proportionality coefficient obtained as a result.
In this case, the method of calculating the amount of lubricant to be supplied includes a step of carrying out a trial construction in ground having properties similar to those of the construction target, and determining a relationship between the construction depth in the trial construction and the amount of lubricant used, and a step of setting the amount of lubricant to be supplied based on the determined relationship, the inner circumference of the pile used in the trial construction, the actual construction depth, and the inner circumference of the pile to be used in the actual construction.
A specific example of the method for calculating the amount of lubricant supplied will be described below.

First, prepare a steel pipe A (inner circumference b (m)) and lubricant B for trial construction.
Next, trial construction will be carried out on ground with properties similar to those of the planned construction site, using the same method as in the experiment described above.
Then, the proportionality coefficient a is calculated based on the proportional relationship between the installation depth of steel pipe A in the trial installation and the amount of lubricant B used.

Based on the proportionality coefficient a obtained as described above and the inner circumference b (m) of the steel pipe A, the supply amount V (L) of the lubricant 5 in the actual construction is set so as to satisfy the following formula (6).

In the case where the lubricant 5 is supplied directly to the vicinity of the tip of the pile 1 through the lubricant supply pipe 23 as shown in FIG. 9, the supply amount of the lubricant 5 may be set using the supply speed of the lubricant 5 by the pump, the rotational penetration speed of the pile 1 into the ground, and a predetermined depth to which the pile 1 penetrates from the surface of the ground 3, and the discharge of the lubricant 5 from the lubricant supply pipe 23 may be stopped when the set supply amount is exhausted. Furthermore, in the case where the tip of the pile 1 is to reach the supporting layer, the supply amount of the lubricant 5 may be set using the depth from the surface of the ground 3 to the top of the supporting layer, and the discharge of the lubricant 5 from the lubricant supply pipe 23 may be stopped when the set supply amount is exhausted.

As described above, according to this embodiment, after the pile 1 reaches a predetermined depth, by not supplying the lubricant 5, soil blockage is actively caused in the pile 1 at a predetermined depth in the ground 3, and the bearing capacity of the pile 1 can be improved. Furthermore, when the tip of the pile 1 is to reach the supporting layer, the supply amount of the lubricant 5 is set using the depth to the top end of the supporting layer, and by not supplying the lubricant 5 near the supporting layer, soil blockage is actively caused in the pile at the supporting layer, and the bearing capacity of the pile 1 can be improved.

Experiments were conducted to verify the effects of the pile construction method of the present invention, and the results are described below.
As an example of the present embodiment, a steel pipe having a diameter of 318.5 mm and a plate thickness of 7.9 mm was used as the pile 1, and construction was performed according to the method described in Figs. 1 and 2. As a comparative example, the same steel pipe was constructed by rotary penetration without supplying the lubricant 5. A laser range finder was attached to the leader 9 holding the pile 1, facing vertically downward. The top height of the soil taken into the pile 1 was continuously measured by this laser range finder. Meanwhile, the penetration length of the pile 1 was continuously measured by a function provided on the pile driver 7. The difference between the top height of the soil in the pile 1 and the depth of the tip of the pile was taken as the "length of the soil in the pile."
FIG. 11 shows a graph comparing the length of soil inside the pile relative to the penetration length of the steel pipe, the pushing force required to penetrate the steel pipe, and the rotational torque required to rotate the steel pipe for the invention example (with lubricant) and the comparative example (without lubricant).
The dashed lines in Figures 11(a) to 11(c) show the penetration length when the lubricant 5 stored in the pile in advance is used up in the example of the invention. In other words, it can be determined that the lubricant 5 is supplied between the inner wall of the pile and the soil inside the pile up to a penetration length slightly exceeding 4m, and that the lubricant 5 is not supplied in the deeper range. The point at which the remaining amount of lubricant 5 in the pile 1 becomes 0 is determined as the point at which the lubricant 5 is used up.

As shown in Figure 11 (a), in the comparative example (without lubricant), the expansion of the soil inside the pile decreases from about a penetration length of 1.5 m. This indicates that soil blockage begins to occur inside the pile from about a penetration length of 1.5 m. Also, as shown in Figures 11 (b) and 11 (c), as the expansion of the soil inside the pile decreases, the pushing force and rotational torque increase, indicating that construction resistance increases due to soil blockage occurring inside the pile.

On the other hand, in the example of the invention (with lubricant), the soil inside the pile continues to expand stably until the penetration length reaches the position of the dashed line, that is, while the lubricant 5 is being supplied, and it can be seen that soil blockage inside the pile is prevented. The pushing force and rotation torque are also stable at low values, and the construction resistance is also small.
In the example of the present invention, after the penetration length exceeds the broken line position, that is, after the supply of the lubricant 5 is stopped, the extension of the soil inside the pile decreases and the pushing force and the rotation torque also increase. This indicates that the lack of supply of the lubricant 5 causes soil blockage inside the pile.

As described above, according to this embodiment, it has been demonstrated that by rotating and penetrating the pile 1 while supplying the lubricant 5 between the inner wall of the pile 1 and the soil inside the pile 1, it is possible to prevent soil blockage inside the pile 1 and reduce construction resistance. It has also been demonstrated that by not supplying the lubricant 5 after a specified depth, soil blockage can be actively caused at the end of construction (after the tip of the pile 1 reaches the specified depth), thereby improving the bearing capacity performance of the pile 1.

REFERENCE SIGNS LIST 1 pile 3 ground 5 lubricant 7 pile driver 9 leader 11 excavation member 13 water tank 15 mixer 17 pump 19 piping 21 mixing element 23 lubricant supply pipe

Claims (4)

A method for constructing a pile, comprising the steps of: supplying a lubricant having a static viscosity higher than that of water and a shear-thinning property that reduces viscosity when subjected to shear force between an inner wall of the pile and soil and sand contained within the pile when a tubular pile is rotary-driven into the ground;
A pile construction method, characterized in that the permeability coefficient k (m/s) of the lubricant in the ground satisfies the following formula (3), and the ratio of the viscosity coefficient (Pa s) of the lubricant according to the shear rate satisfies the following formula (4).
k＜1× ^10-5 ...(3)
(μ´/μ)＜1× ^10-1 ...(4)
μ: Viscosity coefficient of the lubricant at a shear rate of 0.01 (1/s) or less at a temperature of 15 degrees Celsius μ´: Viscosity coefficient of the lubricant at a shear rate of 2.5 (1/s) or less at a temperature of 15 degrees Celsius The pile construction method according to claim 1, wherein the lubricant is supplied from the lubricant stored inside the pile. 3. A pile construction method as claimed in claim 1 or 2, characterized in that after the pile reaches a predetermined depth in the ground, the pile is rotated and penetrated without supplying the lubricant, thereby actively causing soil blockage within the pile . 3. The pile construction method according to claim 1, wherein the supply amount V(L) of the lubricant is set so as to satisfy the following formula (1):
19.4・π・D _in・(H-10D _out )≦V≦19.4・π・D _in・(H+5D _out ) ... (1)
Where, H: Distance from the ground surface to a given depth (m)
D _out : Outer diameter of pile (m)
D _in : Inner diameter of pile (m)

Images