JP6436051B2 - How to build cast-in-place piles - Google Patents

Description

  The present invention relates to a method for constructing a cast-in-place pile.

  As a method for constructing a cast-in-place pile with no soil removal, Patent Document 1 discloses that “a steel pipe pile made of a short pipe with inclined blades attached thereto, and torque can be transmitted to the steel pipe pile by connecting means and in the axial direction” A step of screwing and embedding a winged steel pipe member comprising a casing removably connected to the ground, a step of building a reinforcing bar or a concrete pillar in the winged steel pipe member, and a step of building the reinforcing bar or the concrete pile A cast-in-place pile comprising a step of placing or injecting concrete or a solidifying agent into a winged steel pipe member, and a step of pulling out a casing during or after placement of the concrete or the like "Construction method" has been proposed (see claim 3 of Patent Document 1).

  In addition, as another example of a method for constructing a soil-free pile, Patent Document 2 discloses that “the tip of a steel pipe provided with a spiral blade along the outer periphery in the vicinity of the tip is moved upward and rotated with respect to the steel pipe. The bottom plate provided with the excavating blade is mounted, the load transmission shaft to the bottom plate is inserted into the steel pipe, and the load transmission of the bottom plate is locked by the load transmission shaft. The separation from the shaft is prevented, and then a rotational force is applied to the steel pipe to allow the steel pipe to sink to the support layer with the lowering of the bottom plate and the load transmission shaft, and then by the load transmission shaft to the bottom plate. Unlocking, applying a pressing force to the bottom plate by the load transmission shaft, then pulling up the load transmission shaft, lowering the steel core into the steel pipe and placing concrete, as a casing A construction method of cast-in-place piles characterized by removing the used steel pipe has been proposed (patent text) See claim 1 of 2).

Japanese Patent Laid-Open No. 2003-184078 JP 09-224068 A

In the invention disclosed in Patent Document 1, a steel pipe pile having inclined wings attached to the tip of the casing is left in the ground. Therefore, a new steel pipe pile is required every time construction is performed, and the cost increases. There is.
Further, in the invention disclosed in Patent Document 2, a bottom plate is attached to a steel pipe provided with a spiral blade, and the steel pipe is rotated and penetrated while the bottom plate is held by a load transmission shaft. As described above, in order to prevent the bottom plate from being detached when the steel pipe is rotated and penetrated, the load transmission shaft must be inserted into the steel pipe while being rotated, and there is a problem that workability is poor.
Furthermore, Patent Document 2 requires a process of rotating the steel pipe to a predetermined depth and then pulling up the load transmission shaft and inserting the steel core material. In this sense, there is a problem that workability is poor.

  This invention is made | formed in order to solve this subject, and it aims at providing the construction method of the cast-in-place pile which can reduce the cost of the member newly needed for every construction while being excellent in workability. .

(1) A method for constructing a cast-in-place pile according to the present invention is a method for constructing a cast-in-place pile in which a cast-in-place pile is constructed with no soil using a casing provided with a spiral blade near the tip,
A rotation penetration step of rotating and penetrating the casing into the ground while closing a bottom plate removably installed at the lower end of the casing while closing the tip of the casing;
Inserting a reinforcing bar rod into the casing;
A concrete placing step of placing concrete in the casing in which the reinforcing bar is inserted;
A bottom plate separating step of pressing the concrete in the casing downward from the upper end side of the casing and separating the bottom plate at the tip of the concrete from the casing before the placed concrete solidifies;
And a casing drawing step of drawing the casing before the placed concrete is solidified.

(2) In the above (1), the bottom plate is held by the casing by a holding structure,
The holding structure is provided at at least two locations on the outer periphery or inner periphery of the casing and has horizontal through holes, and at least two locations on the peripheral edge on the upper surface side of the bottom plate. A locking piece having a hole, and a pin inserted through the through hole of both the locking portion and the locking piece in a state where the locking portion and the locking piece are arranged so as to contact each other in the rotation direction. It is characterized by.

(3) Moreover, in the thing as described in said (1) or (2), it has the vertical supporting force confirmation process which confirms the vertical supporting force of a cast-in-place pile before the said rotation penetration process,
The vertical bearing capacity confirmation step includes
A main body made of a steel pipe, a spiral wing provided at the front end of the main body, a bottom plate provided to close the front end opening at the front end of the main body, and the front end fixed to the upper surface side of the bottom plate An inner cylinder made of a steel pipe fixed to a support plate provided on the inner surface of the main body at the other end, a strain gauge for measuring axial strain generated in the inner cylinder, and strain generated in the inner cylinder by the strain gauge And using a pile vertical bearing capacity confirmation device having a computing device for computing the penetration resistance Pp generated in the bottom plate based on the strain,
The vertical support force of the pile is confirmed based on the penetration resistance Pp calculated by the arithmetic device while screwing the vertical support force confirmation device into the ground to be measured.

(4) Moreover, in the above-mentioned (1) or (2), it has a vertical supporting force confirmation step of confirming the vertical supporting force of the cast-in-place pile before the rotational penetration step.
The vertical bearing capacity confirmation step includes
A main body made of a steel pipe, a spiral wing provided at the front end of the main body, a bottom plate provided to close the front end opening at the front end of the main body, and the front end fixed to the upper surface side of the bottom plate The first end is provided on the peripheral surface of the upper end portion of the main body, and the other end of the main body is used to measure the axial strain of the corresponding portion of the main body. A strain gauge, a second strain gauge provided on the upper peripheral surface in the vicinity of the wing portion of the main body to measure axial strain of the part of the main body, and a second strain gauge provided on the peripheral surface of the inner cylinder. The indentation force Po is calculated based on the measurement value of the third strain gauge that measures axial strain and the first strain gauge, and the propulsion force Pw of the blade is calculated based on the measurement value of the second strain gauge. The penetration resistance Pp is calculated based on the measured value of the third strain gauge, and these Po Pw, using the value of Pp, the skin friction Pf generated in the body, using a vertical supporting force confirmation apparatus of piles and a calculation device for calculating the Pf = Pw-Pp + Po,
The vertical support force of the pile is confirmed based on the penetration resistances Pp and Pf calculated by the calculation device while screwing the vertical support force confirmation device into the ground to be measured.

(5) Further, in the above described (4), the pushing force Po is calculated based on the measured value by measuring the original pressure of the jack that pushes the main body into the ground instead of the measured value of the first strain gauge. It is characterized by doing so.

In the present invention, the rotation penetration step of rotating and penetrating the casing into the ground with the bottom plate removably installed at the lower end of the casing while closing the tip of the casing,
Reinforcement rod insertion process for inserting a reinforcing bar rod into the casing, a concrete placing step for placing concrete in the casing in which the reinforcing rod rod is inserted, and the casing before the concrete placed is solidified A bottom plate separating step of pressing the concrete in the casing downward from the upper end side of the casing to separate the bottom plate at the tip of the concrete from the casing, and a casing extracting step of pulling out the casing before the placed concrete is solidified. Since it is not necessary to support the end obturator with a separate member during construction, it is excellent in workability and the work of cutting off the holding of the bottom plate to the casing can be done by pushing in the concrete, so construction is easy In this sense, it is excellent in workability. Furthermore, only the bottom plate is left in the ground, and there is an effect that an increase in cost can be suppressed.

It is explanatory drawing of the construction method of the cast-in-place pile which concerns on one embodiment of this invention. It is explanatory drawing of the casing used for the construction method of the cast-in-place pile shown in FIG. FIG. 3 is a partially enlarged view of a casing, which is one of the members shown in FIG. It is sectional drawing which follows the arrow AA line of FIG. It is a figure which expands and shows the A section enclosed with the circle of FIG. It is a figure which expands and shows the B section enclosed with the circle of FIG. It is explanatory drawing of the other aspect of the holding structure of a baseplate. It is a figure which expands and decomposes | disassembles and shows the C section enclosed with the circle of FIG. It is explanatory drawing of the vertical support force confirmation apparatus of the pile used for the support capacity confirmation method of the pile which is 1 process of other embodiment of this invention.

[Embodiment 1]
Some members used for the construction method of the cast-in-place pile which concerns on one embodiment of this invention are demonstrated based on FIGS.
As members used in the method for constructing a pile according to the present embodiment, a steel casing 3 (see FIG. 2) provided with a spiral blade 1 in the vicinity of the lower end portion, a bottom plate 5 for closing the lower end of the casing 3, and a bottom plate 5 as a casing. There is a holding structure 9 (see FIGS. 3 and 4) of the bottom plate 5 held on the 3 side.
Hereinafter, each member will be described in detail.

<Casing>
The casing 3 is formed of a steel pipe in which the spiral blade 1 is welded in the vicinity of the tip, and its outer diameter is, for example, φ400 mm to φ600 mm. Further, a protrusion 7 for transmitting a rotational force is provided at the upper end of the casing 3.
A bottom plate 5 is held at the tip of the casing 3 so as not to be detached from the casing 3 during the rotation penetration of the casing 3.

<Bottom plate>
The bottom plate 5 is held at the lower end of the casing 3, and prevents earth and sand from entering the casing 3 while the casing 3 is rotating and penetrating.
The bottom plate 5 is formed of a disc whose outer diameter is set larger than the inner diameter of the casing 3.
Since the outer diameter of the bottom plate 5 is set to be larger than the inner diameter of the casing 3, the end portion of the casing 3 is placed on the upper surface of the bottom plate 5 when the bottom plate 5 is held in the casing 3 as shown in FIG. The For this reason, since the bottom plate 5 is pressed against the casing 3 by earth pressure at the time of rotation penetration, the holding force for holding the bottom plate 5 to the casing 3 may be weak.
ing.
Further, the bottom plate 5 also has a function of obtaining a tip support force by pressing the lower ground when pressing the concrete in the casing downward in the bottom plate separation step described later.

<Bottom plate holding structure>
As shown in FIGS. 4 to 6, the holding structure 9 for the bottom plate 5 is a rectangular plate formed on the outer periphery of the lower end portion of the casing 3 and has two locking portions 13 having through holes 11 formed on the bottom plate 5. The casing 3 and the bottom plate 5 are connected to each other by inserting the pin 19 into the locking piece 15 and the locking portion 13.
The holding structure 9 will be described in more detail.

On the outer periphery of the lower end portion of the casing 3, rectangular locking portions 13 are provided at four locations in the circumferential direction (see FIG. 4). And the through-hole 11 of the horizontal direction is formed in the latching | locking part 13 (refer FIG. 5).
On the other hand, two locking pieces 15 are installed at positions corresponding to the locking portions 13 in the bottom plate 5 so as to form a gap into which the locking portions 13 can be inserted. 17 is formed (see FIGS. 4, 5, and 6).
By inserting the locking portion 13 of the casing 3 into the gap between the locking pieces 15 of the bottom plate 5 and inserting the pins 19 into the through holes 11 of the locking portion 13 and the through holes 17 of the locking pieces 15, the casing 3 And the bottom plate 5 are connected by a pin 19.

The operation of the holding structure 9 for the casing 3 and the bottom plate 5 configured as described above will be described. When the casing 3 is rotated while the bottom plate 5 is held in the casing 3 when the casing 3 is rotated and penetrated into the ground, the locking portion 13 provided on the casing 3 comes into contact with the locking piece 15 of the bottom plate 5. , They rotate together without being separated and they do not separate.
Further, when the casing 3 moves downward, the bottom plate 5 is pressed against the tip of the casing 3, so that the bottom plate 5 is not separated from the casing 3. Further, during the rotation penetration, the casing 3 may be moved in the vertical direction. At that time, when it is moved upward, a force is applied to the bottom plate 5 to leave the casing 3. The movement is restricted by the pins 19 and they are not separated. In addition, when the casing 3 moves upward, the force for separating the bottom plate 5 and the casing 3 is small, so that the pin 19 only needs to be strong enough to resist this small force.
As described above, since the casing 3 and the bottom plate 5 are held by the holding structure 9 as described above, when the casing 3 rotates and penetrates, a load is applied to the inside of the casing 3 as in the example of Patent Document 2. Even if the transmission shaft is inserted and the bottom plate 5 is not held, both are not separated.
In addition, since the pin 19 connecting the casing 3 and the bottom plate 5 is broken by a weak force, the casing 3 and the bottom plate 5 can be easily separated.

In the above example, the locking portion 13 is provided on the casing 3 and the locking piece 15 is provided on the bottom plate 5 side. However, the locking portion 13 is provided on the bottom plate 5 as shown in FIGS. The stop piece 15 may be provided on the casing 3 side.
Further, the locking portion 13 or the locking piece 15 provided on the casing 3 side may be provided not on the outer peripheral surface of the casing 3 but on the inner peripheral surface.

A method for constructing a cast-in-place pile using the casing 3, the bottom plate 5, and the holding structure 9 will be described. The method for constructing a cast-in-place pile includes a rotary penetration process, a reinforcing bar punching process, a concrete placing process, a bottom plate separating process, and a casing drawing process.
Hereinafter, each process will be described in detail.

<Rotational penetration process>
The rotation penetration step (FIG. 1A) is a step in which the casing 3 is rotationally penetrated into the ground with the bottom plate 5 held at the tip (see FIG. 3) and penetrates to a predetermined depth with the support layer. Since the bottom plate 5 is held in the casing 3 by the holding structure 9 during the rotation penetration, the bottom plate 5 is not detached from the casing 3 by the movement in the rotation direction at the time of the rotation penetration or the vertical movement. Therefore, earth and sand do not enter the casing 3.
Thus, by allowing the casing 3 to rotate and penetrate, it is possible to penetrate the ground without any soil.

<Rebar rod insertion process>
The reinforcing bar rod insertion step (FIG. 1B) is a step of inserting the reinforcing rod rod 23 into the casing 3 whose tip is penetrated to the support layer.

<Concrete placing process>
The concrete placing step (FIG. 1C) is a step for placing concrete 25 in the casing 3 in which the reinforcing bar 13 is inserted.

<Bottom plate separation process>
In the bottom plate separation step (FIG. 1 (d)), the concrete 25 in the casing 3 is pressed downward from the upper end side of the casing 3 before the cast concrete 25 is solidified, so that the bottom plate 5 at the tip of the concrete is moved to the casing 3. It is the process of separating from.
Specifically, as shown in FIG. 1 (d), a piston member 26 having substantially the same diameter as the inner diameter of the casing 3 is disposed on the upper portion of the casing 3, and the piston member 26 is pressed downward by a jack 27. Then, the concrete 25 in the casing 3 is pushed in. As a result, the concrete 25, which is an incompressible fluid, pushes down the bottom plate 5, thereby destroying or deforming the pin 19 connecting the bottom plate 5 and the lower end of the casing 3, and disconnecting the connection between the bottom plate 5 and the casing 3 by the pin 19 Release.

<Case extraction process>
The casing extraction step (see FIG. 1 (e)) is a step of extracting the casing 3 from the ground while rotating the casing 3 in the direction opposite to the rotation direction at the time of rotation penetration before the concrete 25 is solidified.
The cast-in-place pile 29 is completed by solidifying the concrete 25 with the casing 3 pulled out (see FIG. 1 (f)).

As mentioned above, according to the construction method of the cast-in-place pile of this Embodiment, the cast-in-place pile 29 can be constructed easily. Further, since the bottom plate can be held without being supported by the load transmission shaft as in Patent Document 2 during the rotation penetration of the casing 3, the workability is excellent.
Furthermore, since the work of cutting off the holding of the bottom plate 5 to the casing 3 can be performed by pressing the concrete 25, the construction is simple, and in this sense, the workability is excellent.

[Embodiment 2]
In the case of cast-in-place piles where concrete is hardened on-site, the loading test to confirm the vertical bearing capacity is not possible unless the concrete is hardened. There is a problem that the test is not possible.
For this reason, when it is found that the vertical bearing capacity is insufficient in the loading test conducted after the construction, there is also a problem that the number of piles can be increased more than the original plan, so that only a response by so-called additional piles can be taken.

From the above circumstances, there is a request to confirm the vertical bearing capacity of the pile when the pile is constructed before the cast-in-place pile is constructed.
Therefore, the present embodiment provides a method for constructing a cast-in-place pile including a step of confirming the vertical supporting force of the pile before the rotational penetration step described in the first embodiment.

The construction method of the cast-in-place pile according to the present embodiment has a vertical support force confirmation step of confirming the vertical support force of the pile when the cast-in-place pile is constructed prior to the rotary penetration process of the first embodiment. is there.
First, the pile vertical support force confirmation device 31 used in the vertical support force confirmation method will be described with reference to FIG.
The basic shape of the pile vertical supporting force confirmation device 31 is the same as that of a steel pipe pile, and a main body 33 made of a steel pipe, a spiral wing 35 provided at the front end of the main body 33, and a front end of the main body 33. A bottom plate 37 provided so as to close the tip opening of the main body 33 at a position 1 to 2 cm below the tip portion, a tip is fixed to the upper surface side of the bottom plate 37, and the other end is an inner circumference of the main body 33. And an inner cylinder 41 made of a steel pipe fixed to an annular plate 39 provided on the surface.

Further, the pile vertical supporting force confirmation device 31 is provided on the peripheral surface of the upper end portion of the main body 33 to measure the strain in the axial direction of the portion of the main body 33, and the wing portion 35 of the main body 33. The second strain gauge 45 is provided on the inner peripheral surface of the inner cylinder 41 to measure the axial strain of the relevant part of the main body 33, and the axial strain of the inner cylinder 41 is provided on the inner peripheral surface of the inner cylinder 41. And a third strain gauge 47 to be measured.
Further, the pushing force _Po is calculated based on the measured value of the first strain gauge 43, the propulsive force P _{w of the} blade is calculated based on the measured value of the second strain gauge 45, and the measured value of the third strain gauge 47 is calculated. The calculation device 49 is provided for calculating the penetration resistance P _p based on the above and calculating the peripheral frictional force P _f generated in the main body 33 using the values of P _o , P _w , P _p .
As shown in FIG. 9, the pile vertical supporting force confirmation device 31 preferably includes a display unit 51 that displays a calculation result of the calculation device 49.
Each configuration will be described below.

<Main body>
The main body 33 is made of a steel pipe having an outer diameter of, for example, φ400 mm to φ600 mm. The wing part 35 is welded in the vicinity of the tip of the main body 33, and the main body 33 is rotated and penetrated into the ground by the propulsive force of the wing part 35.
A protrusion (not shown) is provided on the outer peripheral surface of the upper end portion of the main body 33, and a rotational force is applied to the protrusion.

<Wings>
The wing part 35 gives a propulsive force to the main body 33, and is constituted by, for example, a spiral wing.

<Bottom plate>
The bottom plate 37 has a function of blocking the tip opening of the main body 33 and preventing earth and sand from entering the main body 33 when the main body 33 rotates and penetrates.
In order to exhibit this function, the area of the bottom plate 37 may be equal to or slightly larger than the opening of the tip of the main body 33, but the bottom plate 37 also has a function of receiving a ground reaction force for calculating the tip support force. Therefore, it is desirable that the bottom plate 37 be equivalent to the tip opening of the main body 33 from the viewpoint of exhibiting these functions.

<Inner cylinder>
The inner cylinder 41 is made of a steel pipe made of the same material as that of the main body 33, and supports the bottom plate 37 at a position away from the front end by 1 to 2 cm from the front end. A bottom plate 37 is fixed to the lower end side of the inner cylinder 41, and an upper end of the inner cylinder 41 is fixed to an annular plate 39 provided on the inner peripheral surface of the main body 33.
The upper end side of the inner cylinder 41 may be fixed to a support plate provided so as to be connected to the inner peripheral surface of the main body 33 without being fixed to the annular plate 39.

<Strain gauge>
The first strain gauge 43 is provided on the inner peripheral surface of the upper end portion of the main body 33 and measures the strain in the axial direction of the portion of the main body 33.
A pressing force for allowing the main body 33 to penetrate into the ground is applied to the upper end portion of the main body 33, and the indentation force can be obtained by measuring an axial strain caused by the pressing force.
In the present example, the first strain gauges 43 are installed one by one (one pair of installations) at positions that are 180 degrees apart from the main body 33 in the circumferential direction and have the same axial direction. Thus, the bending strain can be canceled and the axial strain can be accurately measured.
Since it is generally considered that the strain gauges are disconnected, two or more pairs may be provided.
In this example, the first strain gauge 43 is provided on the inner peripheral surface of the main body 33, but may be provided on the outer peripheral surface of the main body 33. When provided on the outer peripheral surface, it may be protected from being damaged by an external force. Even if the first strain gauge 43 is provided on the outer peripheral surface, since the wiring passes through the inside of the main body 33, it is necessary to provide a hole for passing the wiring in the main body 3. In this case, the position of the hole is kept away from the installation position of the first strain gauge 43.
The same applies to the second strain gauge 45 and the third strain gauge 47, which will be described later, with respect to the installation positions and the number of installed strain gauges as described above.

The second strain gauge 45 is provided on the inner peripheral surface of the upper portion of the main body 33 in the vicinity of the wing portion 35 and measures the strain in the axial direction of the portion of the main body 33. The position of the second strain gauge 45 in the main body 33 in the axial direction is between the wing portion 35 and the annular plate 39, and is preferably in the vicinity of an intermediate position between the two. By setting the intermediate position between the two, the influence of both ends can be reduced.
When the wing part 35 is rotated while the main body 33 is rotating and penetrating, the soil is scooped up by the wing part 35 and the scooped up soil is pushed upward along the upper surface of the wing. Then, the pushed up soil is gradually compacted, and a propulsive force is generated in the wing portion 35 by the reaction force of the soil. At this time, since a downward tensile force acts on the upper portion of the main body 33 in the vicinity of the wing portion 35 via the wing portion 35, the wing portion is measured by measuring the strain generated in the portion of the main body 33 by the tensile force. 35 driving forces can be determined.

The third strain gauge 47 is provided on the inner peripheral surface of the inner cylinder 41 and measures the axial strain of the inner cylinder 41. The position of the third strain gauge 47 in the inner cylinder 41 in the axial direction is between the bottom plate 37 and the annular plate 39 and is preferably in the vicinity of the intermediate position between the two. By setting the intermediate position between the two, the influence of both ends can be reduced.
When the main body 33 rotates and penetrates, a ground reaction force acts on the bottom plate 37, and the inner cylinder 41 receives a compressive force by the ground reaction force. Therefore, the ground reaction force can be obtained by measuring the strain generated in the inner cylinder 41.

<Calculation device>
Arithmetic unit 49, based on the measurement values of the first strain gauge 43 calculates the pushing force P _o, based on the measurement value of the second strain gauge 45 calculates the thrust P _w of the blade, a third strain gauge 47 The penetration resistance P _p is calculated on the basis of the measured value, and the peripheral friction force P _f generated in the main body 33 is calculated using the values of P _o , P _w , and P _p .
The details of the calculation method of P _o , P _w , and P _p in the calculation device 49 will be described in detail in the description of the vertical support force confirmation step described later.

<Display section>
The display unit 51 displays the calculation result of the calculation device 49. By providing the display unit 51, when the main body 33 is rotating and penetrating, the vertical supporting force of the pile at an arbitrary depth during the propulsion of the main body 33 can be confirmed.

Next, the vertical supporting force confirmation process which confirms the vertical supporting force of a pile using the vertical supporting force confirmation apparatus 31 of the pile comprised as mentioned above is demonstrated.
The vertical supporting force confirmation device 31 of the pile is erected on the ground to be confirmed and rotated, and a propulsive force is generated in the wing portion 35 and screwed into the ground.
During the rotation penetration, each strain gauge outputs a measured value, which should be recorded.
When the vertical force balance confirmation device 31 of this pile is screwed into the ground, the balance of the forces in the vertical direction is expressed by the following equation (1).
P _w + P _o ≧ P _p + P _f (1)
here,
P _w is the driving force P _f cause soil wings scooped by rotating the reaction force upon the clamping solidified soil by pushing up upward along the upper wing surface to the blade portion 35 the main body 33 and the friction of the ground The resistance P _p is a ground penetration resistance P _o generated in the bottom plate 37, and is a pushing force applied to the main body 33.

Similar to general piles, P _p and P _f are determined in accordance with the strength and depth of the soil in contact.
In addition, _Pw also works to draw the pile vertical supporting force confirmation device 31 into the ground while changing the size according to the strength and depth of the soil in contact with Pw. The propulsive force of the wing portion 35 also functions to reduce the penetration pressure of the bottom plate 37 by reducing the upper pressure of the ground in contact with the bottom plate 37.
These results, although piles only vertical bearing force confirmation device 31 mainly thrust wings 35 of the pile is gradually penetrated into the ground, P _p and P _f of penetration resistance is greater than the wing thrust P _w and you will not be able to penetrate, adding the shortfall as P _o.

From the above, the vertical bearing force that the pile to be finally constructed receives from the ground in advance by _calculating the values of P _w , P _p , Po during rotation penetration of the pile vertical bearing confirmation device 31 Can be confirmed.
As described above, the force P _o Push applied to the body 33 can be determined by using the measured values of the first strain gauge 43 as an axial force of the body 33.
Further, thrust P _w of the wings 35 can be determined using the measurement value of the second strain gauge 45.
Further, the penetration resistance P _{p of the} ground can be obtained using the measurement value of the third strain gauge 47 as the axial force of the inner cylinder 41.
Further, the frictional resistance P _f between the main body 33 and the ground can be obtained from P _f = P _w −P _p + P _o by modifying an equation obtained by equalizing the inequality sign of the equation (1).

Here, how to obtain P _w , P _p , P _o and P _f will be described.
The outer diameter of the steel pipe constituting the main body 33: D ₁ , the thickness: t _1, and the outer diameter of the steel pipe constituting the inner cylinder 41: D ₂ , and the thickness t ₂ .
Cross-sectional area _{A 1} of the steel pipe constituting the body ^{_{33,: A 1 = πD 1 2}} /4-π (D 1 -2t 1) a ^{_{2/4 = πt 1 (D}} 1 -t 1).
Further, the cross-sectional area _{A 2} of the steel pipe constituting the inner cylinder 41 is: a ^{_{A 2 = πD 2 2/4}} -π (D 2 -2t 2) 2/4 = πt 2 (D 2 -t 2).

The measured value of the first strain gauge 43 is ε ₀ , the measured value of the second strain gauge 45 is ε _w , and the measured value of the third strain gauge 47 is ε _p, and the Young's modulus of the steel pipe constituting the main body 33 and the inner cylinder 41 Is E, the axial stress σ ₀ of the part of the main body 33 where the first strain gauge 43 is attached is σ ₀ = E · ε ₀ , and the axis of the part of the main body 33 where the second strain gauge 45 is attached. The directional stress σ _w is σ _w = E · ε _w , and the axial stress σ _p of the portion of the inner cylinder 41 to which the third strain gauge 47 is attached is σ _p = E · ε _p .

Then, using these σ ₀ , σ _w , and σ _p , the pushing force P ₀ applied to the main body 33 is P ₀ = σ ₀ · A ₁ , and the propulsive force P _w generated in the wing portion 35 from the reaction force of the soil is , P _w = σ _w · A ₁ , and the ground penetration resistance P _p generated in the bottom plate 37 can also be obtained as P _p = σ _p · A ₂ .
Further, as described above, frictional resistance _{P f} of the main body 33 and the ground _can be determined from _{P f = P w -P p +} P o.

The vertical support force of a pile determined from the ground is generally expressed as "tip support force" + "circumferential friction force".
The tip support force is obtained as the penetration resistance P _p , and the peripheral friction force is obtained as the friction resistance P _f described above.
Therefore, the penetration resistance P _p and the friction resistance P _f are appropriately obtained by screwing the pile vertical supporting force confirmation device 31 of the present embodiment into the ground, and thereby the vertical support of the pile at a predetermined depth. You can check the power.

Note that the tip support force is proportional to the square of the pile diameter, and the circumferential friction force is proportional to the pile diameter. As described above, the vertical support force of the pile is generally “tip support force” + “circumference Since it is expressed by “surface friction force”, if “tip support force” and “circumferential friction force” cannot be obtained individually, in other words, “tip support force” and “circumferential friction force” If the distribution is not known, the vertical bearing capacity when the pile diameter changes cannot be obtained.
In this regard, the pile vertical support force confirmation device 31 of the present embodiment can individually determine the tip support force and the peripheral friction force, and determine P ₀ , P _w , and P _p as unit areas, respectively. Since it can be converted into a per load, “vertical support force” in piles having the same placement depth and different pile diameters can be calculated from the measured values of P ₀ , P _w , and P _p .

Therefore, even if it is a case where the diameter of the main body 33 in the vertical bearing capacity confirmation device 31 of a pile cannot be made the same as the pile diameter planned by the planned main construction, the pile diameter of the main construction is determined from the measured value. In this case, the “circumferential friction force” and the “tip support force” can be calculated separately.
For example, if it is found that the expected vertical bearing capacity cannot be secured with the initial planned pile diameter, the "peripheral friction force" and "tip bearing capacity" when the pile diameter for this construction is increased If it is calculated, or if it is found that an excess vertical bearing force can be expected that exceeds the expected value, calculate the "frictional surface friction force" and "tip support force" when the pile diameter for this construction is reduced. Therefore, it is also possible to perform an appropriate pile design without excess or deficiency before this construction.
In this way, by being able to derive P _p and P _f individually, in addition to verifying that there is no shortage of the planned pile diameter, check the vertical bearing capacity when the pile diameter is the same when the placement depth is the same. Is possible.
In addition, since it is inefficient to create a new pile vertical bearing capacity confirmation device 31 that matches the pile diameter for each site, the vertical bearing capacity confirmation device 31 for piles with a similar diameter that was previously produced and used is reused. You can also

In the above description, as the vertical support force of the pile, it is decided to check the vertical support force of the pile in consideration of both the peripheral friction force and the tip support force. Of the obtained values, Pile design may be considered only with the tip support force. (In this case, it means not expecting the peripheral friction.)
In the above description, an example of measuring with strain gauges to P _o, may be obtained based on the P _o the measured value of the jack source pressure.

An actual operation method of the pile vertical supporting force confirmation device 31 according to the present embodiment will be described.
(1) Take the zero point of the strain gauge before entering the rotation.
(2) Pile vertical bearing capacity confirmation device 31 is rotated into the ground. In the meantime, the arithmetic unit 49 always outputs the measurement value and displays it on the display unit 51 or records it.
(3) The pile vertical bearing capacity confirmation device 31 is rotated and penetrated to a predetermined depth. In addition, when the expected vertical bearing force can be confirmed before reaching the planned depth, it is preferable to proceed at the planned depth.
On the other hand, even if the expected vertical support force is not reached even if the planned depth is reached, the completion is made when the rotation penetrates to the planned depth.
(4) The pile vertical bearing capacity confirmation device 31 is reversely rotated and recovered from the ground.
(5) Based on the measured values, determine the number of pile constructions, pile diameter, etc.

  In the above description, the process is completed when the rotational penetration is made to the planned depth. However, the rotational penetration may be further advanced while monitoring the measured value until the expected vertical support force is obtained.

  As described above, according to the present embodiment, since the pile supporting force that can be expected before constructing cast-in-place piles can be confirmed, it is not necessary to take measures such as increasing the number of piles after constructing cast-in-place piles. Excellent in properties.

DESCRIPTION OF SYMBOLS 1 Spiral wing 3 Casing 5 Bottom plate 7 Protrusion 9 Holding structure 11 Through-hole (locking part)
13 Locking portion 15 Locking piece 17 Through hole (Locking piece)
19 Pin 23 Reinforcing bar 25 Concrete 26 Piston member 27 Jack 29 Cast-in-place pile 31 Vertical support force confirmation device 33 Main body 35 Wing 37 Bottom plate 39 Ring plate 41 Inner cylinder 43 First strain gauge 45 Second strain gauge 47 Third strain Total 49 arithmetic unit 51 display unit

Claims (5)

It is a construction method of a cast-in-place pile that constructs a cast-in-place pile without soil using a casing having a spiral wing in the vicinity of the tip,
A rotation penetration step of rotating and penetrating the casing into the ground while closing a bottom plate removably installed at the lower end of the casing while closing the tip of the casing;
Inserting a reinforcing bar rod into the casing;
A concrete placing step of placing concrete in the casing in which the reinforcing bar is inserted;
A bottom plate separating step of pressing the concrete in the casing downward from the upper end side of the casing and separating the bottom plate at the tip of the concrete from the casing before the placed concrete solidifies;
A method for constructing a cast-in-place pile, comprising: a casing extracting step of extracting the casing before the placed concrete is solidified. The bottom plate is held in the casing by a holding structure;
The holding structure is provided at at least two locations on the outer periphery or inner periphery of the casing and has horizontal through holes, and at least two locations on the peripheral edge on the upper surface side of the bottom plate. A locking piece having a hole, and a pin inserted through the through hole of both the locking portion and the locking piece in a state where the locking portion and the locking piece are arranged so as to contact each other in the rotation direction. The cast-in-place pile construction method according to claim 1, wherein Having a vertical supporting force confirmation step for confirming the vertical supporting force of the cast-in-place pile before the rotation penetration step,
The vertical bearing capacity confirmation step includes
A main body made of a steel pipe, a spiral wing provided at the front end of the main body, a bottom plate provided to close the front end opening at the front end of the main body, and the front end fixed to the upper surface side of the bottom plate An inner cylinder made of a steel pipe fixed to a support plate provided on the inner surface of the main body at the other end, a strain gauge for measuring axial strain generated in the inner cylinder, and strain generated in the inner cylinder by the strain gauge And using a pile vertical bearing capacity confirmation device having a computing device for computing the penetration resistance Pp generated in the bottom plate based on the strain,
The place according to claim 1 or 2, wherein the vertical supporting force of the pile is confirmed based on the penetration resistance Pp calculated by the arithmetic device while screwing the vertical supporting force confirmation device into the ground to be measured. How to build a pile. Having a vertical supporting force confirmation step for confirming the vertical supporting force of the cast-in-place pile before the rotation penetration step,
The vertical bearing capacity confirmation step includes
A main body made of a steel pipe, a spiral wing provided at the front end of the main body, a bottom plate provided to close the front end opening at the front end of the main body, and the front end fixed to the upper surface side of the bottom plate The first end is provided on the peripheral surface of the upper end portion of the main body, and the other end of the main body is used to measure the axial strain of the corresponding portion of the main body. A strain gauge, a second strain gauge provided on the upper peripheral surface in the vicinity of the wing portion of the main body to measure axial strain of the part of the main body, and a second strain gauge provided on the peripheral surface of the inner cylinder. The indentation force Po is calculated based on the measurement value of the third strain gauge that measures axial strain and the first strain gauge, and the propulsion force Pw of the blade is calculated based on the measurement value of the second strain gauge. The penetration resistance Pp is calculated based on the measured value of the third strain gauge, and these Po Pw, using the value of Pp, the skin friction Pf generated in the body, using a vertical supporting force confirmation apparatus of piles and a calculation device for calculating the Pf = Pw-Pp + Po,
The vertical support force of the pile is confirmed based on the penetration resistances Pp and Pf calculated by the calculation device while screwing the vertical support force confirmation device into the ground to be measured. How to build cast-in-place piles.   5. The place according to claim 4, wherein the pushing force Po is calculated based on the measured value by measuring the original pressure of the jack that pushes the main body into the ground instead of the measured value of the first strain gauge. How to build a pile.