JP3220444B2 - Construction method of rotary press-fit steel pipe pile - Google Patents

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 steel pipe pile of a rotary press-fit type, in which a blade-like steel plate is attached to the tip of a steel pipe.

[0002]

2. Description of the Related Art As for construction management in a method of applying a rotating force to a rotary press-fitting steel pipe pile having a blade-shaped steel plate at the tip of a steel pipe to penetrate into the ground, the relationship between input energy at the time of construction and tip resistance has been derived. A construction management formula shown in Japanese Patent Application No. Hei 11-054783 has been proposed. This is to measure the tip resistance Rp while measuring the torque, penetration amount and overload during construction.
Are calculated at the same time, and it is determined whether or not stopping is possible using the Rp value as a criterion in construction management. Japanese Patent Application 11
The tip resistance value Rp shown in -054783 is as follows. _{Rp = [2πTb 0 + Lb {} (1-c) S + cP + απDw '} - QwhπDw' -QwvS] / {(1-c) S + cP + απ (Dp '+ Dw')} (1) Explanation of Symbols rp: penetration resistance of the bottom plate portion ( kN) Tb ₀ : Torque acting on pile tip (kN · m) Lb: Overlay load acting on pile tip (kN) c: Coefficient determined by upward forced deformation of blade S: Penetration per rotation (m) P : The pitch of the blade (m) Dw ': The diameter of the working circle of the blade (the circle on which the resultant force acts in the rotating direction) (m) Dp': The diameter of the working circle of the bottom plate or the bottom plate (m) Qwh: The resistance of the horizontal cutting edge (kN) Qwv: Vertical edge resistance (kN) α: Coefficient of friction between the ground and blades (steel plate)

[0003] In addition to the above, there is a construction management method using torque in the past, but an equation directly related to the ground strength has not been derived, and only a qualitative change has been confirmed. The torque varies greatly depending on the construction conditions, but the conventional construction management method using torque cannot quantitatively evaluate this variation.

On the other hand, in order to construct a building or the like on the ground stably, it is necessary that the supporting force of the press-fitting pile is obtained as designed, but the embedding length necessary to guarantee the designed supporting force is required. Is described as follows: The "Building Foundation Structure Design Guidelines" states that for embedded piles, "In the case of a support pile, it is desirable that the depth of penetration into the support layer is about 1-2 times the pile diameter." It states, "It is desirable that the length of the burial into the support layer is 1 m or more in a place under normal ground conditions." In addition, in the specification of the road bridge, "the permissible bearing capacity of the pile" is set as "the ultimate bearing capacity (Qd) of the pile tip is reduced when the embedding depth is less than 5d. The effect is taken into account. "For cast-in-place piles," the tip of the pile must penetrate into the high-quality support ground to the extent of the pile diameter. " Shall be described. " For the above reasons, it is considered that all piles need to be embedded in the support layer, and the embedding of the pile diameter is required (for steel pipe piles with feathers, about the feather diameter ≒ twice the pile diameter). ing. In the rotary press-in method, each company performs stop control by depth control, and as shown in FIG. 3 , the depth of penetration into the support layer is 1 Dw (Dw is the blade diameter) or more. In addition, regarding the blockage effect at the tip of the pile,
In the case of open-ended piles, the tip closing efficiency is considered to be a problem. "The closing efficiency is determined by the length of penetration into the support layer, η = (apparent tip supporting force of open-ended pile) / (tip supporting force of closed-ended pile) η = 0.16 Lb / Di, 2 ≦ Lb / Di ≦ 5 η = 0.8, 5 <Lb / Di Lb: Depth of penetration into the support layer (m), Di: inside diameter of pile (m) ” The relational expression is shown. For this reason, it is customary for an open-end pile to have a large embedding depth (Lb> 5Di).

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application No. 11-0 is disclosed.
The formula for calculating the tip resistance value Rp shown in US Pat. No. 5,478,833 is complicated because the unknown coefficients α and c and the transmissivity atr (a in Japanese Patent Application No. 11-054783) exist in the formula. The results of the ground survey (soil test) and the shape of the pile to be constructed (blade diameter, blade pitch) were uniform, and the construction manager had to be sufficiently familiar with the construction characteristics of the rotary press-fitting pile. Further, since the Rp value is obtained by inputting the data at the time of construction, it is managed while calculating. In this construction management, the possibility of stopping is determined based on the output obtained from the construction result, which makes it difficult to make predictions in construction and is difficult to handle in construction management.

[0006] Further, with respect to the depth of penetration of the pile into the support layer, the supporting force of the pile is originally determined by the ground strength.
It turns out that it does not depend on the depth of embedding.
However, each standard requires that the length of the pile be deeper, because it is difficult to determine the support layer in the conventional method, and if the length of the pile is longer, the pile tip will become harder. This is based on the grounds that it is more likely to be reached, resulting in more reliable tip support. Generally, the support layer has irregularities, and it is very difficult to detect the support layer by depth management, and the reliability is poor. There is also a construction method that detects using a combination of torque and the like, but it has not been possible to quantitatively evaluate the ground strength.

[0007] Further, as a problem when actually inserting a steel pipe pile into the ground, there are the following points in the prior art. Time and energy (rotational power, excavation power) are required for embedding into the support layer, and the number of works that can be performed in one day is limited. Also, in the case of the rotary press-fitting method, if the rooting is attempted in a state where the torque is insufficient, the penetration amount will always be small,
The penetration is made while disturbing the support layer, and the installation situation is extremely bad. Since the support layer is a firm ground, in the case of impact or rotary press-fitting, if the tip of the pile is not designed to be strong, the tip of the pile may be broken, which tends to be uneconomical. In the case of cast-in-place piles and embedded piles, it is difficult to determine that the tip has reached the support layer, and a large penetration is required as a means to ensure that the pile has been embedded. Because
There is much waste.

According to the present invention, in order to advantageously solve the above-mentioned problems of the conventional steel pipe pile, the relationship between the torque value which is most easily grasped in the construction management, the N value representing the strength of the ground, and the tip supporting force Qu. Rotating press-fit steel pipes with open and closed ends, enabling the selection of appropriate heavy equipment and the determination of the support layer that obtains the designed bearing capacity, and minimizing the length of the pile tip. An object of the present invention is to provide a construction method of a pile.

[0009]

Means for Solving the Problems The present inventor has disclosed Japanese Patent Application No. Hei 11
Developing the equation shown in -054783, conducting construction tests at the same time, accumulating and analyzing data, and leading to a simple equation that is practically effective. The method for constructing a rotary press-fit steel pipe pile according to the first aspect of the present invention is a method for constructing a rotary press-fit steel pipe pile having a blade-like steel plate at the tip and being rotationally press-fitted into the ground. Value), the torque value required at the time of construction is calculated by the following equation. Tt = a · N · Dp ^m −b · Lt · Dp Tt: Torque (kN · m) Dp: Pile diameter (m) Lt: Overhead load (kN) N: N value obtained from standard penetration test a, b, m: coefficient and exponent (where m is 2-3)

[0010] Further, the construction method of the rotary press-fit steel pipe pile according to the second aspect of the present invention is characterized in that a torque required for the construction is calculated by the following equation and an appropriate rotary press-fit steel pipe pile construction machine is selected. . ^{Tt = a · N · Dp m} Tt: Torque (kN · m) Dp: pile diameter (m) N: obtained from SPT N values a, m: factor, and index (where m is 2-3)

According to a third aspect of the present invention, there is provided a method for constructing a rotary press-fit steel pipe pile, comprising calculating a tip support force (Qu) from a torque value acting on a heavy equipment at the time of construction by the following equation, and according to the Qu value. A method for constructing a rotary press-fit steel pipe pile, characterized by controlling the continuation of penetration or the completion of penetration. ^{Qu = X · Dp n · Tt} Qu: tip supporting force (kN) Tt: Torque (kN · m) Dp: pile diameter (m) X, n: coefficient and the exponent (wherein n is 2-m)

According to a fourth aspect of the present invention, there is provided a method for constructing a rotary press-fit steel pipe pile, wherein a blade-like steel pipe is provided at a tip end of the steel pipe pile, and the torque value is calculated by the formula according to claim 1. The tip support force (Qu) is calculated by the formula according to claim 3 to stop the penetration depth of the tip of the pile into the support layer in an amount equal to or less than the blade diameter.

[0013] A method of constructing a rotary press-fit steel pipe pile according to a fifth aspect of the present invention is characterized in that a design support force at the design tip of the rotary press-fit steel pipe pile is calculated by the following equation and used as a construction management target value. Tip support force (kN) = qd · Aw + qdh · Awi qd: αd · Nqdh: qdh = αh · NL·L / Dp However, when L> 5Dp and in the case of a closed end pile , L / Dp = 5. : Tip support force coefficient of blade part (Aw part) αh: Tip support force coefficient of closed soil and sand part (Awi part) or bottom plate part (Awi part) L: Length of penetration into support layer (m) N: Tip N value Aw: locate the area of the outer wing ^{(m 2), Aw = π} · (Dw 2 -Dp 2) / 4 Awi: bottom plate find area ^{(m 2), Awi = π} · Dp 2/4 Dw: Blade diameter (m) Dp: pile diameter (m)

[0014]

Embodiments of the present invention will be described with reference to the drawings. 1A is a front view of a rotary press-fit steel pipe pile according to the present invention, FIG. 1B is a vertical sectional explanatory view of the same, FIG. 2 is a lower perspective view of the rotary press fit steel pipe pile, and FIG. FIG. 3B is a schematic view showing a penetration mechanism of a rotary press-fitting pile and a penetration completed state in the method, and FIG.
FIG. 4 is a cross-sectional view showing a state in which a rotating effect press-fitting steel pipe pile according to the present invention is provided with a closing effect promoting projection, FIG. 5 is a sectional view taken along line AA in FIG. 4, and FIG. FIG. 7 is a plan view of the front view of the press-fit steel pipe pile. 8 is a lower perspective view of a rotary press-fit steel pipe pile having a closed end according to the present invention, FIG. 9 is a lower perspective view of a two-bladed rotary press-fit steel pipe pile also having a closed end, and FIG. It is a downward perspective view of a steel pipe pile. FIG. 11 is a lower perspective view showing the state of the bottom plate excavating blade of the closed-end rotary press-fit steel pipe pile according to the present invention, FIG.
2 is a lower perspective view showing the state of the cutting edge of the closed-end rotary press-fit steel pipe pile of the two blades. The symbols used in the drawings are as follows. Dw: Blade outer diameter (m) Dwi: Blade inner diameter (m) Dp: Rotary press-fit steel pipe pile outer diameter (m) Dpi: Rotary press-fit steel pipe pile inner diameter (m) Tt: Torque (kN · m) acting on pile head : Overlay load acting on the pile head (kN) P: Pitch of blade (m) (reprinted) Symbols other than these are described for each calculation formula, so the collective description is omitted.

A feature of the present invention is that a torque value, a tip support force, and the like necessary for construction are calculated by using a predetermined formula before actual construction. It should be noted that the ground strength N value is grasped from the ground survey result before construction. The present inventor developed the equation (1) shown in Japanese Patent Application No. 11-054783 and derived the relationship between the torque that is most easily grasped in the construction management and the N value representing the strength of the ground. In the equation (1), the following is considered. -When construction is performed so that the penetration amount S at the time of hitting is substantially equal to the pitch P of the blade, S ≒ P, and (1-c) S + cP = (1-c) P + cP = P. energy consumption Qwh · π · Dw '= 2π · Qwh · (Dw' / 2) = 2πTb by _wh Tb _wh: torque and can be expressed by the horizontal edge resistance, 2πTb ₀ in relation to the energy consumption 2PaiTb ₀ by the torque - Taking 2πTb _wh = 2πTb, Tb = Tb ₀ −Tb _wh・ The energy consumption due to the resistance of the vertical cutting edge is so small that it is neglected. Therefore, the expression (1) becomes as follows. Rp = {2πTb + Lb (P + απDw ′)} / {P + απ (Dp ′ + Dw ′)} (1) ′ P adopts the function of Dp, and Dp ′ and Dw ′ are D
It is a function of p and is expressed as P = g · Dp g: Coefficient for determining blade shape Dp ′ = 2/3 · Dp Dw ′ = {2 (h ³ −1)} / {3 (h ² −1)} · Dp = i · Dph: Blade diameter ratio = Dw / Dpi = {2 (h ³ -1)} / {3 (h ² -1)} Therefore, the equation (1) ′ shows that the penetration resistance Rp is equal to the torque Tt and Tb.
Tb, Lt using the relationship of
And the pile diameter Dp can be arranged as follows. Tb = atr · Tt, Lb = atr · Lt atr: torque Tt, overburden transmissibility _{Rp = X 1 · Tt / Dp} + Y 1 · Lt to pile the lower end of the load _{Lt (2) X 1 = 2π} · atr / { (2/3 + i) α · π + g｝ Y ₁ = atr (i · α · π + g) / ｛(2/3 + i) α · π + g｝ X ₁ and Y ₁ are coefficients derived from the shape and construction parameters of the pile. Required from construction records. On the other hand, since Rp represents the supporting force at the bottom plate found portion, it has a relationship proportional to the average N value and the bottom plate area. However, in the case of a rotary press-fit open-end pile, the dependence of the cutting edge resistance and the bottom plate resistance changes depending on the ground conditions as the diameter changes, and in the case of large-diameter piles, the blockage rate of the soil inside the pipe becomes a factor. It was found that the behavior of the soil in the pipe and the resistance of the blades were related and were proportional to the bottom plate area or pile diameter. (In some cases, it is proportional to the area of the pile, but it is proportional to the area.) Rp = α1 · N · Dp ^1-2 (3) α1: Tip support force coefficient Therefore, from equations (2) and (3), Tt and N Value, Lt, Dp
The following relationship is derived between. ^{α1 · N · Dp 1~2 = X} 1 · Tt / Dp + Y 1 · Lt ∴ Tt = (α1 · N · Dp 1~2 - Y 1 · Lt) · Dp / X 1 Tt = a · N · Dp ^m− b · Lt · Dp (4) m = 2−3 a = α1 / X ₁ , b = Y ₁ / X _{1 As} is clear from the equation (4), the torque is proportional to the average N value from the first term. However, it can be said that Dp is proportional to the second to third powers. Further, since the second term is negative, it can be seen that the overload has the effect of reducing the torque during construction, and that the required torque increases if no overload is applied.

On the contrary, when selecting a heavy machine, it is determined that the required torque will be increased if the load on the vehicle is neglected, so that the capacity of the selected heavy machine can be given a margin. Can be determined. In order to selection of heavy machinery from above to remove the second item of the equation (4), Tt = a · N · Dp m (5) N: an N value obtained from ground survey results.

The basis of the tip support force Qu used for construction management is as follows. Since the relationship between the torque and the ground strength N value is as shown in equation (4), the tip support force can be estimated from the obtained N value. ^{Tt = a · N · Dp m} -b · Lt · Dp derived from the equation, soil strength N derived from the torque
Is, N = (Tt + b · Lt · Dp) / (a · Dp m) (6) N: N value tip supporting force calculated from torque and overburden load is proportional to the tip area is proportional to the ground intensity N value since the relationship of (6) and the tip Qu from the supporting force of the relationship = α1 · N · a = α1 · (Tt + b · Lt · Dp) / (a · Dp m) · f · Dp 2 = X · Dp n1 · Tt + Y · Lt · Dp n2 (7) a: the tip area ^{(m 2) = π · Dp} 2/4 · {1+ (h 2 -1) e} = f · Dp 2 e: supporting force coefficient at the blade effective rate Tt: torque (kN · m) Lt: overburden load (kN) [alpha] 1: front end supporting force coefficient X: X _1, f from calculated constant = α1 · f / a = α1 · f / (α1 / X 1) = f · X ₁ Y: constant obtained from Y ₁ and f = α 1 · b · f / a = α 1 · (Y ₁ / X ₁ ) · f / (α 1 / X ₁ ) = f · Y ₁ n1: n2 = 2 −m n2: n2 = 3-m can be derived . As can be seen from the relational expression of the equation (7), applying the overlying load Lt has the effect of increasing Qu, but generally the overlying load is the load required when the layer changes, and Since the blade penetrates with the propulsive force of the blade when penetrating into the vehicle, there is no need to perform an operation of applying an overload greater than its own weight. By ignoring the two items of the overload, Qu can be evaluated on the safe side. Therefore, the two items in the expression (7) are deleted and the expression for deriving the relationship of the tip support force from the torque is used. In this case, the error of the overlaid load corresponding to the own weight becomes very small and may be considered to be included in X. Qu = ^{X · Dp n · Tt (8} ) n becomes n = 2-m (9) . From the above, the stop is managed by the equation (8). At the time of construction, there is a design Qu value set as a stop value, and reaching the value is a stop condition. In addition, the stopping condition may be determined based on the torque value converted from the design Qu value.

When concretely implementing the present invention using the above formula, the coefficients and indices need to be clear. The following numerical values were obtained from the construction tests performed so far. Index m 2.5 to 3 when steel pipe pile diameter is small diameter (609.6φ or less) 2 to 2.5 when steel pipe pile diameter is large diameter (609.6φ or more) It changes stepwise according to the pile diameter), and is closely related to the pipe diameter and the blockage effect. Coefficient a It depends on pile shape and construction parameters. The records of the construction performed by the inventors are as follows. When reaching the support layer 30 to 40 Penetration of 1Dp into the support layer 40 to 60 Penetration of 2Dp to the support layer 60 to 80 Penetration of 2Dp or more to the support layer 80 to 100a exhibits a closing effect as the penetration depth increases and the bottom plate portion It is a coefficient that reflects the effect of compacting the ground below and the phenomenon that the ground hardness of the upper surface of the blades relatively increases, that is, a coefficient that depends on the depth of embedding.

An example of mathematical calculations required for the actual penetration of the rotary press-fitting pile 1 according to the present invention will be described with reference to FIGS. Steel pipe pile 1 pile diameter Dp 600φ, outer diameter Dw of blade 2 =
The predicted torque for penetrating a 1.5 Dp rotary press-fitting pile through an intermediate layer of N = 30 and a layer thickness of 2 Dp and embedding 1 Dp into a support layer of N = 50 is 600φ, so m = 2.5 intermediate than the thickness passing through the layers 2Dp, than embedment depth 1Dp to _{a 1 = 70 ∴ Tt = a} 1 · N 1 · Dp m = 70 · 30 · 0.6 2.5 = 586 kN · m supporting layer, a = 52 ∴Tt = a · N · Dp m = 52 · 50 · 0.6 2.5 = 725 kN · m Therefore, if selected construction machine to meet the capacity for putting roots to the support layer, it is construction.

Next, steel pipe pile 1 pile diameter Dp 600φ, blade 2
Of a rotary press-fitting pile having an outer diameter Dw1.5Dp of N = 50 on a support layer is considered. For this pile, the design tip bearing capacity is calculated to be 4505 kN. In the construction of this pile, the torque became 800 kN · m when the penetration into the support layer was laid about 1.5 Dp. That is, from a = 57, X = f ・ X ₁ = π / 4 ｛{1 + e (h ² -1)}｝ α1 / a = 4.46 (From the results of the loading test, e = 0.5, α1 = 200 is ^2-2.7 · 800 = 5101 kN thus guided are) thus ^{Qu = X · Dp n · Tt} = 4.46 · 0.6, which satisfies the design supporting force. (Design supporting force is 4240kN, X = 4.46 Thus from a = 57, expect Uchidome torque Tt = Qu / (X · Dp n) = 4240 / (4.46 · 0.6 2-2.7) = 664 .8 kN ・ m Therefore, stopping at 800 kN ・ m is appropriate.)

By employing the above construction management method, the capacity of the heavy equipment can be selected in advance from the ground strength N value. Therefore, according to the present invention, it is possible to adopt a construction method with good construction efficiency, high quality, and excellent cost performance.
Also, with regard to the driving torque, it is possible to determine whether or not driving can be performed for all the piles while observing the fluctuation of the torque, so that a highly reliable pile can be formed.

Next, the support layer 4 of the tip portion 2 of the rotating steel pipe pile 1
The depth of embedding in the groove will be described with reference to FIGS. In the conventional rotary press-fitting pile, as described above, the penetration into the support layer is about 1 Dw or more (Dw is the outer diameter of the blade 3). This is to ensure that the tip of the pile is firmly rooted in the support layer, and the bottom face receiving the supporting force is regarded as the effective diameter in the conventional rotary press-fitting pile with blades. In the case of the rotary press-fit steel pipe pile of the present invention, as described above, the management of the support layer by the torque acting on the heavy equipment is extremely easy and can be quantitatively determined. Therefore, it is possible to reduce the penetration into the support layer. Specifically, the depth can be reduced from about the blade pitch to about 1 Dp.

[0023] Due to the small rooting length, the effect of closing the pile inside may not be expected. When the diameter of the steel pipe pile is large (600φ or more) or when it is difficult to evaluate the blocking effect even with a small diameter, blockage inside the pile may not be obtained and insufficient supporting force may occur. As a supplement,
A bladed steel pipe with protruding blades is used inside the pile shown in FIG. 2, or a vane provided with a plugging effect promoting projection on the pile inner wall 1 a shown in FIGS. The problem is solved by closing the pile internal space 8 using a steel pipe. In the steel pipe pile with vanes shown in FIG. 2 in which the vanes are extended inside, the supporting force can be added by increasing the blade area of the inside 8 of the pile, so that the supporting force can be obtained even if the internal soil is not closed. In this case, the blockage effect of the earth and sand does not matter, and the management becomes easy to satisfy the design specifications. In the embodiment, a donut-shaped steel plate having an outer diameter approximately 1.5 to 2.0 times the outer diameter of the pile steel pipe and an inner diameter 0.3 to 0.9 times the inner diameter of the pile steel pipe was used. The degree of blockage of the pile internal space due to the blade area for obtaining the design tip supporting force can be selected in advance according to the pile diameter, the state of the ground, and the like, so that the construction can be easily managed.

As shown in FIGS. 4 to 7, in the case of a steel pipe pile with blades provided with a plugging effect promoting projection 7 on the pile inner wall 1a for promoting the blockage of earth and sand entering the steel pipe, as an embodiment, as shown in FIG. A protrusion 7 is provided on the inner wall of the steel pipe pile at a height of about 0.5 to 2.0 times the inner diameter 1a of the steel pipe. The degree of blockage of the pile internal space by the blockage-promoting projection for obtaining the design tip supporting force can be selected in advance according to the pile diameter, the state of the ground, and the like, so that the construction can be easily managed. The shape of the blockage-promoting protrusion 7 may be an annular shape shown in FIG. 4 or an arc shape. Also, as shown in FIGS. 6 and 7, a plurality of rectangular projections are formed.
It may be fixed to the inner wall. Since the tip is open, the penetration is excellent, while the tip is closed with a small amount of rooting, so that the energy required for construction can be suppressed and the bearing strength can be sufficiently high.

It is also effective to use a pile with a closed tip shown in FIGS. 8 to 10 to reduce the depth of the support layer. When the pile with the closed tip is deeply laid into the support layer, the amount of penetration per rotation becomes small and disturbs the support ground, but with a small piercing as in the present invention,
Since the earth and sand corresponding to the pile volume can be easily moved to the side, the effect of pressing the ground can be obtained, and the condition of the supporting ground in the stopped state can be maintained in a healthy state. In addition, the bearing has sufficient bearing capacity, and it is possible to construct a high-quality pile. In this embodiment, the shape of the blade is a donut-shaped steel plate having an outer diameter approximately 1.5 to 2.0 times the outer diameter of the steel pipe pile. FIG. 8 shows a case where one place of a donut-shaped steel plate is cut and spirally welded and fixed to an end side wall of a steel pipe pile. Fig. 9 shows the same donut-shaped steel plate cut at two places, one at the end of the steel pipe pile,
The case where the other one is welded and fixed to the end wall of the steel pipe pile is shown. In FIG. 10, the end of the steel pipe pile is cut into a shape following the shape of the blade-shaped steel plate, a bottom plate surface is provided at the same position as the blade rear end, and the inside of the pile is closed. As described above, although the shapes of the blades are various, a common expression can be applied to the calculation formulas of the torque value and the tip supporting force, and the embedding length of the pile tip can be stopped below the blade diameter.

As described above, regardless of the open-end pile and the closed-end pile,
The shape of the blade is various, and the pile tip also has various shapes. 11 and 12 show the bottom plate 9 at the tip of the pile.
And a bottom excavation blade 10 attached thereto. Fig. 11 shows one blade fixed by welding along the side wall of the steel pipe pile end, and one excavation blade. However, Fig. 12 shows two blades along the side wall of the steel pipe pile end. It is fixed by welding and has two excavating blades. There are many shapes and mounting positions of the bottom surface excavation blade 10 in addition to those illustrated.

A formula for calculating the design tip supporting force in the case where the above-mentioned steel pipe with blades overhanging the inside of the pile is used, or in the case where the pile inner wall 1a is provided with the protrusion 7 for promoting the blockage of the earth and sand that has entered the steel pipe. Is calculated using a formula that takes into account the perimeter area of the blade (the area of the installation surface) and the obstruction of earth and sand that has entered the interior. The coefficient shown in the following equation was obtained from the results of the loading tests performed so far, and it has been confirmed that the coefficient changes depending on the type of the supporting ground. Tip support force (kN) = qd Aw + qdh Awi qd: 100 N-200 Nqdh: 60 N L / Dp However, when L> 5 Dp and for a closed end pile, L / Dp = 5 to L: root entry length to the support layer (m) N: tip N value Aw: locate the area (m ²⁾ of the blade only Awi: area excluding the Aw from finding the area of the blade (m ²⁾ this equation Is the design support force (extreme) of the rotary press-fit steel pipe pile of the present invention, and serves as an index at the time of stopping during construction. At the time of construction, it is sufficient that Qu or torque that satisfies the value obtained by this formula is obtained. The support force obtained by this support force calculation formula varies depending on the N value of the support layer, but is generally satisfied by penetration (penetration) of about the blade pitch.

By using the formula of the design tip supporting force as a target value in determining the penetration stop at the time of construction, the effect of reducing the penetration of the steel pipe pile tip portion 2 and not disturbing the surrounding ground was obtained. . Almost 1 for embedding in the support layer
Penetration of about 2 to 2 rotations is sufficient, especially if the penetration is about the blade pitch, since the pile enters during one rotation, elements that disturb the support layer can be eliminated. Further, the torque required to penetrate and stop the hard support layer is remarkably reduced, and the construction can be performed with a construction machine one rank smaller. Moreover, because the bearing capacity is obtained as before, the effect of not disturbing the ground,
Pile reliability is further improved.

[0029]

The present invention clarifies the relationship between the torque value which is most easily understood in construction management, the N value representing the strength of the ground, and the tip supporting force Qu, and the ground obtained from the ground survey results. From the strength (N value), the required torque value and the tip support force (Qu) can be calculated in advance during construction. Therefore, it is possible to easily select an appropriate rotary press-fit steel pipe pile heavy machine according to the ground condition. In addition, the tip support force (Qu) can be calculated for all the piles to be constructed, and the continuation of penetration or the completion of penetration of the rotary press-fit steel pipe pile can be controlled according to the Qu value. Therefore, it is possible to confirm that all the piles satisfy the design bearing capacity, so that a pile having high reliability can be constructed.

Further, in order to obtain the designed supporting force,
The support layer can be grasped, and the depth of penetration at the tip of the pile can be clarified by construction management. Since the length of the pile tip embedded in the support layer can be stopped below the blade diameter, the penetration amount of the steel pipe pile tip is reduced, and the effect of not disturbing the surrounding ground can be obtained. Since the ground is not disturbed, a pile having a high bearing capacity can be formed.
In terms of construction, the torque required to penetrate the hard support layer and stop is significantly reduced, construction with one rank smaller construction machine is also possible, and cost reduction is possible,
Since the construction can be performed while confirming that there is enough capacity of the heavy equipment to be selected, it is possible to determine a safety aspect in the construction. In addition, since the supporting force can be obtained as before with a small embedding, the cost can be reduced in both the material and the construction. Therefore, according to the present invention, there is an effect that a construction method having good construction efficiency, high quality, and excellent cost performance can be adopted.

[Brief description of the drawings]

FIG. 1A is a front view of a rotary press-fit steel pipe pile according to the present invention, and FIG. 1B is a longitudinal sectional view of the same.

FIG. 2 is a lower perspective view of a rotary press-fit steel pipe pile.

FIG. 3A is a schematic diagram showing a penetration mechanism of a rotary press-fitting pile and a completed penetration state in the construction method of the present invention, and FIG.
FIG. 2 is a schematic view of the related art.

FIG. 4 is a cross-sectional view showing a state in which a clogging effect promoting projection is provided inside the rotary press-fit steel pipe pile according to the present invention.

FIG. 5 is a sectional view taken along line AA in FIG.

FIG. 6 is a front view of a rotary press-fit steel pipe pile having a closing effect promoting projection.

FIG. 7 is a plan view of the same.

FIG. 8 is a lower perspective view of a rotary press-fit steel pipe pile having a closed end according to the present invention.

FIG. 9 is a lower perspective view of the two-blade closed-end rotary press-fit steel pipe pile.

FIG. 10 is a lower perspective view of the closed-end rotary press-fit steel pipe pile.

FIG. 11 is a lower perspective view showing a state of a cutting edge of the closed-end rotary press-fit steel pipe pile according to the present invention.

FIG. 12 is a lower perspective view showing the state of two excavating blades of the closed-end rotary press-fit steel pipe pile.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 steel pipe pile 1 a steel pipe pile inner wall 2 steel pipe pile tip 3 blade 4 ground support layer 5 blade tip 6 blade excavation blade 7 blockage effect promoting projection 8 pile internal space 9 bottom plate 10 bottom plate excavation blade

Continuing on the front page (72) Inventor Tomoki Takeda 2-6-3 Otemachi, Chiyoda-ku, Tokyo Nippon Steel Corporation (72) Inventor Makoto Nagata 2-6-3 Otemachi, Chiyoda-ku, Tokyo New Japan (56) References JP-A-5-163727 (JP, A) JP-A-11-303070 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) E02D 7/22 E02D 5/28 E02D 5/56

Claims (5)

(57) [Claims] 1. A method of constructing a rotary press-fit steel pipe pile having a blade-like steel plate at its tip and being rotationally pressed into the ground, based on a ground strength (N value) obtained from a ground survey result, a torque required at the time of construction. A method for constructing a rotary press-fit steel pipe pile, wherein the value is calculated by the following equation. Tt = a · N · Dp ^m −b · Lt · Dp Tt: Torque (kN · m) Dp: Pile diameter (m) Lt: Overhead load (kN) N: N value obtained from standard penetration test a, b, m: coefficient and exponent (where m is 2-3) By wherein the following equation to calculate the torque required to construction, the construction method Tt = a · N · Dp ^m rotary press fit steel pipe, characterized by selecting an appropriate rotational pressed steel pipe for construction machinery Tt: Torque (kN · m) Dp: Pile diameter (m) N: N value obtained from standard penetration test a, m: Coefficient and index (where m is 2-3) 3. From the torque value acting on the heavy equipment during construction,
A method for constructing a rotary press-fit steel pipe pile, comprising calculating tip support force (Qu) by the following formula, and controlling continuation or completion of penetration of the rotary press-fit steel pipe pile according to the Qu value. ^{Qu = X · Dp n · Tt} Qu: tip supporting force (kN) Tt: Torque (kN · m) Dp: pile diameter (m) X, n: coefficient and the exponent (wherein n is 2-m) 4. A steel pipe pile with vanes provided with a vane-shaped steel plate at the tip thereof and being rotationally press-fitted into the ground, a torque value according to the formula according to claim 1, and a tip supporting force (according to the formula according to claim 3). A method for constructing a rotary press-fit steel pipe pile, characterized in that by calculating Qu), the length of penetration of the pile tip into the support layer can be stopped by an amount equal to or less than the blade diameter. 5. A method for constructing a rotary press-fit steel pipe pile, comprising calculating a design tip supporting force of the rotary press-fit steel pipe pile by the following equation and setting the calculated value as a construction management target value. Tip support force (kN) = qd Aw + qdh Awi qd: qd = αd Nqdh: qdh = αh N L / Dp However, when L> 5 Dp and for a closed-end pile, L / Dp = 5 Αd: Tip supporting force coefficient of blade part (Aw part) αh: Tip supporting force coefficient of closed earth and sand part (Awi part) or bottom plate part (Awi part) L: Length of penetration into support layer (m) N : tip N value Aw: locate the area of the outer wing ^{(m 2), Aw = π} · (Dw 2 -Dp 2) / 4 Awi: bottom plate find area ^{(m 2), Awi = π} · Dp 2/4 Dw: Blade diameter (m) Dp: Pile diameter (m)