JP2011220003A - Quality control method for pile - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quality control method for pile enabling simplified assessment on the soundness of a pile and having high reliability on its assessment.SOLUTION: The soundness of a pile is assessed based on the natural frequency calculated by vibrating the pile buried in the ground. When there are more than one pile buried in the ground, the soundness of each pile may be assessed based on the natural frequency of each pile by vibrating each pile buried in the ground and calculating the natural frequency of each pile.

Description

  The present invention relates to a pile quality control method, and more particularly to a pile quality control method that can easily evaluate the soundness of a pile buried in the ground and can increase the reliability of the evaluation.

  In the construction of structures mainly on soft ground, when it is difficult to support a structure with a shallow foundation, a foundation pile that supports a structure by driving a pile deeply is known. The construction method of these foundation piles includes cast-in-place pile construction method in which a cylindrical reinforcing bar assembled at the site is dropped into the ground drilled and concrete is poured into it to form a pile. There is known a driving pile method for inserting and embedding pre-made piles such as steel pipe piles and concrete piles.

  In recent years, when emphasis is placed on seismic design, piles buried in the ground are required to satisfy not only conventional vertical bearing capacity but also excellent horizontal resistance characteristics. These requirements are not met simply by using sound pile bodies (for example, high-quality concrete and steel pipes), and even when using sound pile bodies, loosening of the ground when constructing the piles The performance will fluctuate under the influence of the above. Therefore, quality control and performance confirmation of piles in the state where they are finally buried in the ground are very strict.For example, in the cast-in-place pile method, the support layer assumed in the design by looking at the earth and sand when excavating the ground There is no other way than to check whether the piles buried in the ground are sound or not. On the other hand, with the driven pile method, although there are comparatively quantitative management indicators such as rebound amount, this management indicator is also only a qualitative confirmation of the vertical bearing capacity, and the pile buried in the ground is healthy. It has not yet been accurately evaluated whether or not there is. Therefore, the quality control of the pile is actually only recorded the process management when constructing the pile and the finished shape at the pile head after construction (pile head pile diameter, pile position, etc.). is the current situation.

  Under such circumstances, recently, as a quality control method of pile bodies, a nondestructive inspection method such as an integrity test (PI test) or the like, as disclosed in Patent Document 1, it was buried to a predetermined depth in the ground. There has been proposed a loading test or the like that twists the head of the pile, measures the torque when the pile starts to rotate, and estimates the maximum peripheral frictional force based on this torque.

JP 2004-225484 A

  However, nondestructive inspection methods such as the integrity test (PI test) have advanced techniques and experience in interpreting the results, and can detect only the presence or absence of defects in the pile body. In addition, according to the loading test disclosed in Patent Document 1, it is possible to verify the presence or absence of ground loosening, but the loading test is expensive and also requires a large amount of preparation. It is virtually impossible to use this method for quality control. Furthermore, since the loading test is basically a destructive inspection, it is not possible to confirm the total number of piles.

  This invention is made in view of such a situation, and provides the quality control method of the pile which can evaluate easily the soundness of the pile embed | buried under the ground, and can improve the reliability with respect to evaluation. This is the main issue.

  The present invention for solving the above problems is a pile quality control method for evaluating the soundness of a pile buried in the ground, and is a natural frequency calculated by vibrating the pile buried in the ground. It is characterized by evaluating the soundness of piles based on

  Moreover, when there are a plurality of piles embedded in the ground, the plurality of piles embedded in the ground are vibrated, the natural frequency of each pile is calculated, and the piles are calculated based on the natural frequency of each pile. It is good also as evaluating every soundness.

  Moreover, it is good also as evaluating the soundness of a pile by comparing the calculated natural frequency and the reference | standard natural frequency preset as a reference value.

  Moreover, when comparing with a reference | standard natural frequency, it is good also as performing a vibration of a pile with a vibrator.

  Moreover, when using a vibrator, you may set a reference | standard natural frequency using the displacement amplitude of the pile vibrated with the vibrator.

  Furthermore, the pile is vibrated with the acceleration amplitude of the vibration generated by the vibration generator being constant, and the acceleration of the vibration pile is measured, and (measured pile acceleration) / (vibration acceleration generated by the vibration generator) On the other hand, the displacement amplitude of the pile may be estimated by performing Fourier spectrum analysis, and the reference natural frequency may be set using the estimated displacement amplitude of the pile.

Further, by dividing the displacement amplitude (X: measured value) at the natural frequency of the pile vibrated by the vibrator by the reference displacement (X ₀ ) of the pile, the displacement amplitude is normalized and the normalized Using the displacement amplitude (X _n ), the horizontal ground reaction force coefficient (K _h ) necessary for setting the reference frequency may be obtained by the following equation (1).

ここで、式（２）中のＥＩは杭の曲げ剛性、ρは杭の密度、Ａは杭の断面積、Ｌは杭の長さ、Ｄは杭の直径、を示す。 Further, the reference natural frequency (ω ₁ ) may be set by the following equation (2) using the horizontal ground reaction force coefficient (K _h ).

Here, EI in the formula (2) is the bending stiffness of the pile, ρ is the pile density, A is the cross-sectional area of the pile, L is the length of the pile, and D is the diameter of the pile.

  According to the present invention, the soundness can be evaluated by the natural frequency of the pile, the soundness of the pile can be easily evaluated, and high reliability is imparted to the pile evaluated by the present invention. Can do.

It is a perspective view which shows an example of the pile embed | buried under the ground. It is a conceptual diagram which shows a mode that a pile is vibrated using a vibrator. (A) shows the waveform of the acceleration amplitude measured by the accelerometer A, and (b) shows the waveform of the acceleration amplitude measured by the accelerometer B. It is a graph which shows the result of having performed the Fourier spectrum analysis with respect to (acceleration of the measured pile) / (acceleration of the vibration generated with a vibrator). It is a figure for demonstrating the boundary conditions for calculating a reference | standard natural frequency.

  Below, the quality control method of the pile of this invention is demonstrated. The present invention is a pile quality control method for evaluating the soundness of a pile buried in the ground, wherein the pile buried in the ground is vibrated, and the pile frequency is calculated based on the natural frequency of the pile calculated thereby. Assess soundness.

  First, the relationship between the natural frequency calculated by vibrating a pile buried in the ground and the soundness of the pile will be described. The horizontal resistance of piles buried in the ground varies depending on the stiffness of the pile body and the ground resistance. These are the natural frequencies in the horizontal direction of the piles buried in the ground (hereinafter simply referred to as natural frequencies). Can be evaluated. In other words, since the natural frequency calculated (measured) by vibrating the pile fluctuates according to the stiffness and ground resistance of the pile body, the soundness of the natural frequency of the pile embedded in the ground is evaluated. It can be used as an indicator.

  The present invention can be applied to all piles embedded in the ground that can excite natural vibration by vibration, for example, ready-made piles embedded in the ground by the driven pile construction method, or built on the ground by the cast-in-place pile construction method Applicable to piles made. The pile driving method is a prefabricated pile (steel pipe pile, filled steel pipe pile, H-shaped steel pile, etc.) that is manufactured in a drill hole formed in the ground and then driven into the ground after being transported to the site. , Reinforced concrete (RC) piles, prestressed concrete (PC) piles, PHC piles, steel concrete (SC) piles, etc.) This is a method of constructing a pile by inserting a reinforcing rod into the borehole and injecting ready-mixed concrete into the excavation hole.

  In particular, according to the present invention, it is possible to objectively evaluate the soundness of a pile based on the natural frequency, and since it is constructed on the spot, the cast-in-place pile method cannot be evaluated in advance. Therefore, it can be particularly suitably applied to the evaluation of the soundness of piles embedded in the ground.

  There is no particular limitation on the method of exciting the natural vibration in the pile buried in the ground, but when the pile is just buried in the ground and only the pile exists in the ground, the natural vibration should be excited by free vibration. I can't. In consideration of such points, it is preferable to excite the natural vibration by forcibly vibrating the pile in the horizontal direction using a vibration device or the like. When vibrating, there is no particular limitation as to which position of the pile the vibration device is installed, and it can be appropriately installed in the vicinity of the pile head. In the case of cast-in-place piles, it is necessary to excavate the ground and excavate the pile head to perform the pile head treatment, but the pile may be vibrated before the pile head treatment. It is good also as vibrating a pile afterwards.

  The vibration device for vibrating the pile is not particularly limited as long as it has a function capable of forcibly vibrating the pile. In the present invention, a vibrator can be used particularly preferably. The exciter is generally as small as 10kg in weight, and it can excite natural vibration simply by installing it at the head of the pile, so the natural frequency can be easily calculated at the site where the pile is buried. Is possible.

  Also, there is no particular limitation on the method of calculating the natural frequency from the natural vibration excited by vibrating the pile. For example, the natural frequency can be specified from the resonance curve and phase spectrum of the natural vibration. More specifically, for example, Japanese Patent Application Laid-Open No. 2009-198366 discloses that the natural frequency is specified by a vibrator although it is intended for a retaining wall, and the method is applied to a pile. can do.

  Next, an example of calculating the natural frequency will be described with reference to FIG. In addition, FIG. 1 is a figure which shows the state by which the several pile 1 was embed | buried under the ground by the cast-in-place pile construction method, a continuous line part shows the part protruded from the ground, and a broken line part shows the inside of the ground. As shown in FIG. 1 (a), in order to vibrate the pile 1 embedded in the ground, a vibrator 10 is installed on the pile 1 (in the case shown in FIG. 1, a reinforcing bar 2). The vibrator 10 is connected to a measuring instrument, an external power source, and the like.

  Here, the vibration is generated by the vibrator 10 installed in the pile, so that the pile 1 is forcibly vibrated and the natural vibration is excited. The excited natural vibration is analyzed by a measuring device connected to the exciter 10, and the natural frequency is calculated. Note that a measuring instrument or the like for calculating the natural frequency does not necessarily have to be connected to the vibrator 10 and may be directly connected to the pile 1.

  Next, a method for evaluating the soundness of a pile based on the natural frequency will be described. Examples of the method for evaluating the soundness of a pile based on the natural frequency calculated by the above method include the methods exemplified in the following (i) to (iii).

  (I) The soundness of the pile can be evaluated by comparing the natural frequency calculated by the above method with a reference natural frequency set in advance as a reference value. The reference natural frequency set as the reference value in advance may be a theoretical value of the natural frequency calculated from design conditions (such as pile specifications and ground physical properties), and damage to the pile body and loosening of the ground may occur. It is also possible to actually measure the natural frequency when there is not, and use this as the reference natural frequency. The “setting of the reference natural frequency” will be described in detail later.

  Here, when the pile body is damaged or when the ground is loose, the natural frequency is lower than the natural frequency when the pile body is not damaged or the ground is not loose. Therefore, the soundness of the piles embedded in the ground can be evaluated according to how much the natural frequency calculated this time has changed with respect to the reference natural frequency.

  (Ii) When there are a plurality of piles buried in the ground, the plurality of piles buried in the ground are vibrated, the natural frequency of each pile is calculated, and the natural frequency of each pile is calculated. By comparing the above-mentioned reference natural frequency, the soundness of each pile can be evaluated.

  (Iii) In (ii), the soundness can be evaluated by a conventionally known statistical method by comparing the natural frequency of each pile without comparing with the reference natural frequency. For example, as shown in FIG. 1, when the pile 1a, the pile 1b, the pile 1c, and the pile 1d are embedded in the ground, the calculated natural frequency of the pile 1b is higher than the natural frequencies of other piles. When it is low, it can be evaluated that the soundness of the pile 1b is low.

(Specific embodiment)
The quality control method of the present invention described above will be described more specifically.

  Drawing 2 is a key map showing signs that a pile is vibrated using a vibrator.

  As shown in FIG. 2, the exciter 20 is installed at the tip of the pile 30, and the accelerometer A for measuring the acceleration of the exciter is installed in the exciter 20. An accelerometer B for measuring the acceleration of the head is installed.

  Here, as described above, there is no particular limitation on the method of calculating (measuring) the natural frequency of the pile 30 by vibrating the pile 30 with the vibrator 20, but for example, as described above Thus, you may apply the method currently disclosed by Unexamined-Japanese-Patent No. 2009-198366.

  In the quality control method according to the present invention, the natural frequency of the pile 30 is calculated (measured), and this is compared with a reference natural frequency that is set in advance as a reference value. It is also characterized by evaluating sex. In setting the reference natural frequency, various assumptions may be made according to the situation of the site where the pile 30 is constructed, and various physical quantities may be used for appropriate calculation. Although the invention is not particularly limited, the inventor of the present application can set the reference natural frequency relatively easily and accurately by using the displacement amplitude of the pile 30 that is vibrated by the vibrator 20. I found.

  In calculating the displacement amplitude of the pile 30, theoretically, the acceleration detected by the accelerometer B installed on the pile head can be calculated by second-order integration, and this method is also used in the present invention. Don't deny doing. However, in view of the fact that the waveform detected by the accelerometer B is very complicated and it is often difficult to easily perform second-order integration in the field, the present inventor has intensively studied and found the following method. It was.

  In other words, the pile 30 is vibrated with the acceleration amplitude of vibration generated by the vibrator 20 constant, that is, the acceleration amplitude measured by the accelerometer A is constant, and the acceleration of the vibrated pile 30 is measured with the accelerometer B. By performing Fourier spectrum analysis on (acceleration of the measured pile) / (acceleration of vibration generated by the exciter), in other words, (acceleration of accelerometer B) / (acceleration of accelerometer A) This is a method of estimating the displacement amplitude of the pile and setting the reference natural frequency using the estimated displacement amplitude of the pile.

  3A shows a waveform of acceleration amplitude measured by the accelerometer A, and FIG. 3B shows a waveform of acceleration amplitude measured by the accelerometer B. FIG.

  As can be seen from FIG. 3A, if the acceleration amplitude of the vibration generated by the vibrator 20 is constant, the acceleration amplitude measured by the accelerometer A is naturally constant (in the case of FIG. 3A). , Approximately 1000 gal). And the acceleration amplitude of the pile head of the pile 30 at this time becomes FIG.3 (b). Here, it is also possible to calculate the natural frequency based on a peak at about 25 seconds.

  FIG. 4 is a graph showing the result of Fourier spectrum analysis for (measured pile acceleration) / (vibration acceleration generated by a vibrator).

  In the method of the present invention, after measuring the acceleration amplitude by the two accelerometers A and B, (measured pile acceleration) / (vibration acceleration generated by the vibrator), in other words, the accelerometer B Of the acceleration) / (acceleration of the accelerometer A).

4, the frequency f _m of the position with a peak P is the natural frequency of the pile 30. Further, in the peak P (acceleration measured pile) / (acceleration of vibration which is generated by exciter), that is, when the peak value of the response magnification B / A to Z, the acceleration amplitude Y of the natural frequency f _m Then, it can be calculated by the following equation (3) using the constant acceleration amplitude _Amax generated by the vibrator.

Then, using the acceleration amplitude Y of the natural frequency f _m of the pile 30, in order to estimate the displacement amplitude X of piles 30 may use the following equation (4).

Furthermore, in the present invention, the displacement amplitude (X: actual measurement value) calculated by the above equation (4) is divided by the reference displacement (X ₀ ) of the pile, thereby normalizing the displacement amplitude and normalizing it. Using the displacement amplitude (X _n ), the horizontal ground reaction force coefficient (K _h ) necessary for setting the reference frequency is obtained by the following equation (1).

Here, K _h0 in the formula (1) is a horizontal ground reaction force coefficient used in the design, and corresponds to a horizontal ground reaction force coefficient when 1% or 10 mm of the pile diameter is set as the reference displacement X _0. . Further, the coefficients “3” and “−2” in the formula (1) are calculated by various tests conducted by the inventors.

  FIG. 5 is a diagram for explaining boundary conditions for calculating the reference natural frequency.

As shown in FIG. 5, a pile of bending rigidity: EI, density: ρ, cross-sectional area: A, length: L, diameter: D is fixed at a depth L (fixed end), and the ground at this time If the horizontal ground reaction force coefficient is K _h (calculated in the above equation (1)), the reference natural frequency (ω ₁ ) can be calculated by the following equation (2).

Note that, as shown in FIG. 5, the above formula (2) is a predetermined boundary condition, that is, the bending rigidity is EI, the density is ρ, the cross-sectional area is A, the length is L, the diameter is It is an expression when it is assumed that the pile whose D is D is fixed at the depth L (fixed end), and therefore, analytically based on the above equation (2), assuming other boundary conditions. The natural frequency (ω ₁ ) may be calculated.

  Thus, according to the above embodiment, the natural frequency can be easily grasped from the acceleration and the acceleration of the vibrating pile by making the acceleration of the vibration applied to the pile by the exciter constant. Furthermore, because the acceleration of vibration applied to the pile by the vibrator is constant, the acceleration amplitude of the pile corresponding to the natural frequency can be easily calculated. Based on these results, the horizontal ground reaction force coefficient can be made to correspond to the displacement amplitude of the pile, and the reference natural frequency can be set based on relatively simple boundary conditions.

  According to the present invention, it is possible to objectively evaluate damage to piles in the ground, loosening of the ground, and the like that cannot be visually evaluated based on the natural frequency, so-called omission. It can be used as a deterrent to construction. Conventionally, since the quality control accuracy for evaluating the soundness of piles is low, it has been necessary to ensure safety in design by considering the safety factor greatly. According to this, it is possible to reduce the safety factor and rationalize the design of the pile.

DESCRIPTION OF SYMBOLS 1,30 ... Pile 2 ... Reinforcement rod 10,20 ... Exciter

Claims (8)

A pile quality control method for evaluating the soundness of piles buried in the ground,
A pile quality control method characterized by evaluating pile soundness based on a natural frequency calculated by vibrating a pile embedded in the ground. When there are multiple piles embedded in the ground,
Each of the piles embedded in the ground is vibrated, and the natural frequency of each pile is calculated.
The pile quality control method according to claim 1, wherein the soundness of each pile is evaluated based on the natural frequency of each pile.   The pile quality control method according to claim 1 or 2, wherein the soundness of the pile is evaluated by comparing the calculated natural frequency with a reference natural frequency set in advance as a reference value. .   The pile quality control method according to claim 3, wherein the pile is vibrated by an exciter.   5. The pile quality control method according to claim 4, wherein the reference natural frequency is set using the displacement amplitude of the pile vibrated by the vibrator.   The pile is vibrated with a constant acceleration amplitude of vibration generated by the exciter, and the acceleration of the vibrated pile is measured, and (measured pile acceleration) / (vibration acceleration generated by the exciter) The pile quality control method according to claim 5, wherein the pile displacement amplitude is estimated by performing a Fourier spectrum analysis, and the reference natural frequency is set using the estimated pile displacement amplitude. The displacement amplitude is normalized by dividing the displacement amplitude (X: measured value) at the natural frequency of the pile vibrated by the vibrator by the reference displacement (X ₀ ) of the pile, and the normalized displacement amplitude The horizontal ground reaction force coefficient (K _h ) required for setting the reference natural frequency is obtained by the following equation (1) using (X _n ): Pile quality control method.

Here, K _h0 in the equation (1) is a horizontal ground reaction force coefficient used in the design. The pile quality control method according to claim 7, wherein the horizontal natural reaction force coefficient (K _h ) is used to set a reference natural frequency (ω ₁ ) according to the following equation (2).

Here, EI in the formula (2) is the bending stiffness of the pile, ρ is the pile density, A is the cross-sectional area of the pile, L is the length of the pile, and D is the diameter of the pile.

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