JP2017078291A - Device and method for confirming vertical bearing capacity of pile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and a method for confirming vertical bearing capacity of a pile capable of accurately confirming the vertical bearing capacity when the pile is constructed before constructing the same.SOLUTION: A device 1 for confirming vertical bearing capacity of a pile comprises: a body 3 made of a steel pile; a spiral blade 5 attached to a tip section of the body 3; a bottom plate 7 installed at the tip section of the body 3 in a manner that closes a tip opening; an inner pipe 11 which is made of a steel pipe with a tip end thereof fixed to an upper face side of the bottom plate 7 and the other end thereof fixed to an annular plate 9 on an inner face of the body 3; a distortion meter which measures distortion of the inner pipe 11 in an axial direction; and a calculation device 19 which calculates penetration resistance Pgenerated on the bottom plate 7 on the basis of the distortion on the inner pipe 11 measured by the distortion meter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus and a method for confirming the vertical supporting force of a pile obtained when the pile is constructed on the ground prior to the construction of the pile before the construction of the pile.

As a method for confirming the vertical bearing capacity of the pile, there is a method of confirming the vertical bearing capacity during pile construction from the hammer ram weight, the fall height, the penetration amount, the rebound quantity, etc. in the hammering method.
However, in the pile construction methods other than the striking construction method, there is no method for confirming the vertical supporting force of the pile before construction or during construction.

  Therefore, for example, a method of confirming by a loading test after construction of a pile is performed. As a specific example, as described in [Prior Art] in Patent Document 1, two or four reaction force piles are placed around a measurement target pile (test pile) and tested. A reaction force girder device having a main beam supported by a reaction force pile and a secondary beam engaged with the main beam above the pile is constructed, and a pressure jack is disposed between the test pile and the main beam. The pressure force is applied to the test pile by the jack so that the reaction force is indirectly engaged with the secondary beam and is received by the plurality of reaction force piles via the tensile material engaged with the reaction force pile. (See paragraphs [0002] to [0003] of Patent Document 1).

JP 2002-47677 A

However, in the case of the method using the loading device as described above, the construction of the reaction force pile is necessary and the construction of the reaction force girder device is necessary, as described in Patent Document 1, The cost of testing and the number of days required for the loading test are a heavy burden on the construction.
In addition, in the case of cast-in-place piles where concrete is hardened on site, the loading test can only be performed after the pile has been hardened. is there.
In addition, when a lack of vertical bearing capacity is found in a loading test carried out after construction, there is also a problem that the number of piles can be increased more than the initial plan, and only so-called additional piles can be taken.

  In view of the above circumstances, it has been desired to develop an apparatus and method that can confirm (predict) the vertical bearing force when a pile is constructed before the pile is constructed.

  This invention is made | formed in order to solve this subject, and provides the vertical bearing capacity confirmation apparatus and method of a pile which can confirm the vertical bearing capacity at the time of constructing a pile accurately before constructing a pile. It is aimed.

(1) The vertical supporting force confirmation device for a pile according to the present invention is configured to block the tip opening at the tip of the main body, a spiral wing provided at the tip of the main body, and the tip of the main body. A bottom plate provided on the inner plate, an inner cylinder composed of a steel pipe having a tip fixed to the upper surface side of the bottom plate and the other end fixed to a support plate provided on the inner surface of the main body, and axial strain generated in the inner cylinder. A strain gauge to be measured, and a calculation device that measures strain generated in the inner cylinder by the strain gauge and calculates a penetration resistance P _p generated in the bottom plate based on the strain. is there.

(2) The pile vertical supporting force confirmation device according to the present invention is such that a main body made of a steel pipe, a spiral wing provided at the front end of the main body, and the front end opening of the main body are closed. Provided on the upper surface of the bottom plate, and the other end is provided on the peripheral surface of the upper end portion of the main body, and an inner cylinder made of a steel pipe fixed to a support plate provided on the inner surface of the main body. A first strain gauge that measures the axial strain of the part of the main body and a second strain that is provided on the upper peripheral surface in the vicinity of the wing portion of the main body and measures the axial strain of the part of the main body And a third strain gauge provided on the peripheral surface of the inner cylinder for measuring the strain in the axial direction of the inner cylinder, and a pushing force _Po is calculated based on the measured value of the first strain gauge, based on the measurement values of 2 strain gauge calculates the thrust P _w of the wing, a total of the third strain gauge Calculating a penetration resistance _{P p} based on the values, these _{P o,} P w, using the values of _{P p,} the skin friction _{P f} generated on the main _body, as _{P f = P w -P p +} P o And an arithmetic device for calculating.

(3) Further, in those described in the above (2), the pushing force P _o, based on the measurement values by measuring the initial pressure of the jacks to push the body to the ground instead of the measured value of the first strain gauge It is characterized by being operated.

(4) The pile vertical supporting force confirmation method according to the present invention is a pile vertical supporting force confirmation method using the pile vertical supporting force confirmation device according to any one of the above (1) to (3). ,
While screwing the vertical supporting force confirmation device into the ground to be measured, the vertical supporting force of the pile is confirmed based on the penetration resistance P _p calculated by the calculation device, or the penetration resistance P _p and the circumferential friction force P _f It is characterized by doing.

In the present invention, a main body made of a steel pipe, a spiral wing provided at the tip of the main body, a bottom plate provided at the tip of the main body so as to close the tip opening, and a tip of the bottom plate An inner cylinder made of a steel pipe fixed to the upper surface side and the other end fixed to a support plate provided on the inner surface of the main body, a strain gauge for measuring axial strain generated in the inner cylinder, and the strain gauge The vertical bearing force when the pile is constructed before the pile is constructed by measuring the strain produced in the inner cylinder and calculating the penetration resistance P _p produced in the bottom plate based on the strain. Can be confirmed with high accuracy.

It is explanatory drawing of the vertical supporting force confirmation apparatus of the pile which concerns on embodiment of this invention.

[Embodiment 1]
A pile vertical supporting force confirmation device 1 according to the present invention will be described with reference to FIG.
The basic shape of the vertical supporting force confirmation device 1 of the pile is the same as that of the steel pipe pile, and a main body 3 made of a steel pipe, a spiral wing part 5 provided at the front end of the main body 3, and a front end of the main body 3 A bottom plate 7 provided so as to close the front end opening of the main body 3 at a position 1 to 2 cm below the front end portion, the front end is fixed to the upper surface side of the bottom plate 7, and the other end is the inner circumference of the main body 3. And an inner cylinder 11 made of a steel pipe fixed to an annular plate 9 provided on the surface.

Further, the pile vertical supporting force confirmation device 1 is provided on the inner peripheral surface of the upper end portion of the main body 3 to measure the strain in the axial direction of the portion of the main body 3 and the wing portion in the main body 3. 5, a second strain gauge 15 provided on the inner peripheral surface of the upper portion of the main body 3 for measuring the axial strain of the body 3, and an axial strain of the inner cylinder 11 provided on the inner peripheral surface of the inner cylinder 11. And a third strain gauge 17 for measuring.
Further, the indentation force _Po is calculated based on the measured value of the first strain gauge 13, the propulsive force P _{w of the} blade is calculated based on the measured value of the second strain gauge 15, and the measured value of the third strain gauge 17 is calculated. The calculation device 19 is provided which calculates the penetration resistance P _p based on the above and calculates the peripheral frictional force P _f generated in the main body 3 using the values of P _o , P _w and P _p .
In addition, as shown in FIG. 1, the pile vertical supporting force confirmation device 1 desirably includes a display unit 21 that displays a calculation result of the calculation device 19.
Each configuration will be described below.

<Main body>
The main body 3 is made of a steel pipe having an outer diameter of, for example, φ400 mm to φ600 mm. The wing part 5 is welded in the vicinity of the tip of the main body 3, and the main body 3 is rotated and penetrated into the ground by the propulsive force of the wing part 5.
A protrusion (not shown) is provided on the outer peripheral surface of the upper end portion of the main body 3, and a rotational force is applied to the protrusion.

<Wings>
The wing | blade part 5 gives a thrust to the main body 3, and is comprised by the spiral wing, for example.

<Bottom plate>
The bottom plate 7 has a function of closing the front end opening of the main body 3 and preventing earth and sand from entering the main body 3 when the main body 3 rotates and penetrates.
In order to exhibit this function, the area of the bottom plate 7 may be equal to or slightly larger than the tip opening of the main body 3, but the bottom plate 7 also has a function of receiving a ground reaction force for calculating the tip support force. Therefore, it is desirable that the bottom plate 7 is equivalent to the opening of the front end of the main body 3 from the viewpoint of exhibiting these functions.

<Inner cylinder>
The inner cylinder 11 is made of a steel pipe made of the same material as that of the main body 3, and supports the bottom plate 7 at the distal end portion of the main body 3 at a position 1 to 2 cm below the distal end portion. The bottom plate 7 is fixed to the lower end side of the inner cylinder 11, and the upper end of the inner cylinder 11 is fixed to an annular plate 9 provided on the inner peripheral surface of the main body 3.
Note that the upper end side of the inner cylinder 11 may be fixed to a support plate provided so as to be connected to the inner peripheral surface of the main body 3 without being fixed to the annular plate 9.

<Strain gauge>
The first strain gauge 13 is provided on the inner peripheral surface of the upper end portion of the main body 3 and measures the axial strain of the part of the main body 3.
A pressing force for allowing the main body 3 to penetrate into the ground is applied to the upper end portion of the main body 3, and the indentation force can be obtained by measuring an axial strain caused by the pressing force.
In this example, the first strain gauges 13 are installed one by one (one pair installation) at positions that are 180 ° apart from the main body 3 in the circumferential direction and the axial direction is the same. The axial strain can be accurately measured by canceling the bending strain.
Since it is generally considered that the strain gauges are disconnected, two or more pairs may be provided.
In the present example, the first strain gauge 13 is provided on the inner peripheral surface of the main body 3, but may be provided on the outer peripheral surface of the main body 3. When provided on the outer peripheral surface, it may be protected from being damaged by an external force. Even if the first strain gauge 13 is provided on the outer peripheral surface, since the wiring passes through the inside of the main body 3, 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 13.
The same applies to the second strain gauge 15 and the third strain gauge 17, which will be described later, with respect to the position and number of strain gauges installed as described above.

The second strain gauge 15 is provided on the inner peripheral surface of the upper portion of the main body 3 in the vicinity of the wing portion 5 and measures the strain in the axial direction of the portion of the main body 3. The position of the second strain gauge 15 in the main body 3 in the axial direction is between the wing portion 5 and the annular plate 9 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 5 is rotated while the main body 3 is rotating and penetrating, the soil is scooped up by the wing part 5, and the scooped up soil is pushed upward along the upper surface of the wing. The pushed-up soil is gradually compacted, and a propulsive force is generated in the wing portion 5 by the reaction force of the soil. At this time, since a downward tensile force acts on the upper portion of the main body 3 in the vicinity of the wing portion 5 via the wing portion 5, the wing portion is measured by measuring the strain generated in the portion of the main body 3 by the tensile force. 5 driving forces can be obtained.

The third strain gauge 17 is provided on the inner peripheral surface of the inner cylinder 11 and measures the axial strain of the inner cylinder 11. The position of the third strain gauge 17 in the inner cylinder 11 in the axial direction is between the bottom plate 7 and the annular plate 9 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 main body 3 rotates and penetrates, a ground reaction force acts on the bottom plate 7, and the inner cylinder 11 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 11.

<Calculation device>
Arithmetic unit 19, based on the measurement values of the first strain gauge 13 calculates the pushing force P _o, it calculates the thrust P _w wings based on the measurement value of the second strain gauge 15, a third strain gauge 17 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 3 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 19 will be described in the second embodiment described later.

<Display section>
The display unit 21 displays the calculation result of the calculation device 19. By providing the display unit 21, when the main body 3 is rotating and penetrating, the vertical supporting force of the pile at an arbitrary depth during the propulsion of the main body 3 can be confirmed.

[Embodiment 2]
Next, a method for confirming the vertical supporting force of the pile using the pile vertical supporting force confirmation device 1 configured as described above will be described.
The vertical supporting force confirmation device 1 for piles is erected on the ground to be confirmed and rotated, and a propulsive force is generated in the wing part 5 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 1 for this pile is screwed into the ground, the balance of the force 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 5 friction body 3 and Soil The resistance P _p is the penetration resistance P _{o of the} ground generated in the bottom plate 7 and the pushing force applied to the main body 3.

Similar to general piles, P _p and P _f are determined in accordance with the strength and depth of the soil in contact.
Further, _Pw also works to draw the pile vertical supporting force confirmation device 1 into the ground while changing its size according to the strength and depth of the soil in contact with Pw. The propulsive force of the wing part 5 also serves to reduce the penetration pressure of the bottom plate 7 by reducing the upper pressure of the ground in contact with the bottom plate 7.
These results, although vertical bearing capacity checking apparatus 1 piles mainly piles only thrust of the blade portion 5 gradually penetrates 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 1 Can be confirmed.
As described above, the force P _o Push applied to the body 3 can be determined by using the measured values of the first strain gauge 13 as an axial force of the body 3.
Further, thrust P _w of the wings 5 can be determined using the measurement value of the second strain gauge 15.
Further, the penetration resistance P _{p of the} ground can be obtained using the measured value of the third strain gauge 17 as the axial force of the inner cylinder 11.
Furthermore, the frictional resistance P _f between the main body 3 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 3 is D ₁ , the thickness is t _1, and the outer diameter of the steel pipe constituting the inner cylinder 11 is D ₂ and the thickness is t ₂ .
Cross-sectional area _{A 1} of the steel pipe constituting the main body ^{_{3,: 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 11 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 13 is ε ₀ , the measured value of the second strain gauge 15 is ε _w , and the measured value of the third strain gauge 17 is ε _p, and the Young's modulus of the steel pipe constituting the main body 3 and the inner cylinder 11. Is E, the axial stress σ ₀ of the part of the main body 3 where the first strain gauge 13 is attached is σ ₀ = E · ε ₀ , and the axis of the part of the main body 3 where the second strain gauge 15 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 11 to which the third strain gauge 17 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 3 is P ₀ = σ ₀ · A ₁ , and the propulsive force P _w generated in the wing part 5 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 7 can also be obtained as P _p = σ _p · A ₂ .
Further, as described above, frictional resistance _{P f} of the main body 3 and the ground _{it 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 frictional resistance P _f are appropriately obtained by screwing the pile vertical support force confirmation device 1 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 respect, in the pile vertical support force confirmation device 1 of the present embodiment, the tip support force and the peripheral friction force can be obtained individually, and P ₀ , P _w , and P _p are respectively determined as unit areas. 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 3 in the pile vertical bearing capacity confirmation device 1 cannot be made the same as the planned pile diameter in 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 make a new pile vertical bearing capacity confirmation device 1 that combines the pile diameters at each site, the vertical bearing capacity confirmation device 1 for piles of near diameters that have been produced and used before 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.

The actual operation method of the vertical bearing capacity confirmation device 1 for piles according to the present embodiment will be described.
(1) Take the zero point of each strain gauge before rotating.
(2) Pile vertical bearing capacity confirmation device 1 rotates and penetrates into the ground. In the meantime, the arithmetic unit 19 always outputs the measurement value and displays it on the display unit 21 or records it.
(3) The pile vertical bearing capacity confirmation device 1 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 1 is reversely rotated and recovered from the ground.
(5) Based on the measured value of the vertical bearing capacity of the pile, determine the number of piles to be built, pile diameter, etc.

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

DESCRIPTION OF SYMBOLS 1 Vertical support force confirmation apparatus 3 Main body 5 Wing | wing part 7 Bottom plate 9 Ring plate 11 Inner cylinder 13 1st strain gauge 15 2nd strain gauge 17 3rd strain gauge 19 Calculation apparatus 21 Display part

Claims (4)

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 a calculation device for calculating the penetration resistance P _p generated in the bottom plate based on the strain. 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 measured value of the third strain gauge that measures the axial strain and the first strain gauge, and the propulsive force P _{w of the} blade is calculated based on the measured value of the second strain gauge. And the penetration resistance P _p is calculated based on the measured value of the third strain gauge. _{o, piles P} w, using the values of _{P p,} characterized in that the circumferential surface frictional force _{P f} generated on the main _body, and a computing device for computing a _{P f = P w -P p +} P o Vertical bearing capacity confirmation device. The pushing force P _o, according to claim 2, wherein the main body in place of the measured value of the first strain gauge to measure the original pressure of the jacks to push the ground, characterized in that so as to calculation based on the measured value Pile vertical bearing capacity confirmation device. A method for confirming the vertical bearing capacity of a pile using the vertical bearing capacity confirmation device for a pile according to any one of claims 1 to 3,
While screwing the vertical supporting force confirmation device into the ground to be measured, the vertical supporting force of the pile is confirmed based on the penetration resistance P _p calculated by the calculation device, or the penetration resistance P _p and the circumferential friction force P _f A method for confirming the vertical bearing capacity of a pile, characterized by:

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