Pile evaluation method and evaluation device

Abstract

The present invention provides a pile evaluation method and evaluation apparatus that can evaluate steel pipe piles embedded in the ground. [Solution] The present invention provides a method for evaluating a pile 1 embedded in the ground, wherein the pile is a steel pipe pile having two or more members made of different materials, including a steel pipe and a filling material, and the method includes analyzing the time-domain waveforms of the incident wave and reflected wave observed at the pile head 2 as the pile propagates between the pile head 2 and the pile tip 3 of the pile 1 due to impact with the pile head 2.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for evaluating piles embedded in the ground.

Background Art

[0002] For example, in pile works on slopes or the like, or for existing piles and other piles embedded in the ground during rebuilding of structures, there are cases where it is required to confirm or evaluate whether required resistance force is maintained without pulling the piles out from the ground.

[0003] In such cases, the state such as soundness of the entire pile including the portion buried in the ground is estimated by using the pile head that is exposed from the ground surface or located closest to the ground surface in the ground. Conventionally, as this type of technology, there are those described in Patent Documents 1 to 4, for example.

[0004] Patent Document 1 states that it "provides a pile soundness evaluation method capable of easily determining whether a pile is sound", and describes "a pile soundness evaluation method for evaluating whether the pile is in a sound state by striking the pile head of the pile to generate an elastic wave, and measuring the reflection property of the elastic wave with an accelerometer installed on the pile head, wherein a waveform value a at the pile head, a waveform value b at the cracked portion of the pile, and a waveform value c at the tip portion of the pile are detected from the measurement result of the reflection property, and the soundness of the pile is evaluated based on the value a, the value b, and the value c".

[0005] Patent Document 2 proposes a pile evaluation method with the objective of "providing a method that enables accurate evaluation of the support performance of a pile," which includes "the steps of: obtaining the rise time difference of an actual impact elastic wave test from the time the top of the pile is struck to generate an impact wave, until the impact wave propagates through the pile as an elastic wave and the reflected wave reflected at the lower end of the pile propagates back to the top of the pile as an elastic wave; obtaining the elastic wave propagation speed of the pile; determining the length of an assumed pile; creating an analytical model of the pile and the surrounding ground on which the pile is installed, and calculating the rise time difference of the analytical model assuming that the impact elastic wave test has been performed on the analytical model; determining whether the difference between the rise time difference of the actual impact elastic wave test and the rise time difference of the analytical model is less than or equal to a set value; and determining that the length of the pile is the same as the assumed pile length if the difference between the rise time difference of the actual impact elastic wave test and the rise time difference of the analytical model is less than or equal to a predetermined set value."

[0006] Patent Document 3 discloses a pile evaluation method comprising: "the steps of: obtaining the rise time difference of an actual impact elastic wave test, from the time when the top of the pile is struck to generate an impact wave, until the impact wave propagates through the pile as an elastic wave and the reflected wave reflected at the lower end of the pile propagates to the top of the pile as an elastic wave; obtaining the elastic wave propagation velocity of the pile; determining whether the pile is longer than a predetermined reference value; if the pile is determined to be longer than the reference value, calculating the pile length by reducing the measured value of the elastic wave propagation velocity of the pile; and if the pile is determined to be shorter than the reference value, calculating the pile length using the measured value of the elastic wave propagation velocity of the pile, wherein the calculation of the pile length by reducing the measured value of the elastic wave propagation velocity of the pile is characterized by using the following reduction rate formula or a chart derived from the above formula." According to this "pile evaluation method," "it becomes possible to evaluate the support performance of the pile simply and accurately."

[0007] Patent Document 4 describes a method for evaluating the soundness of a pile, focusing on a "wall-shaped wall pile," which involves "measuring the reflection characteristics of elastic waves generated by striking the pile head of the wall pile at the pile head, performing spectral analysis of the reflection characteristics, and evaluating the soundness of the wall pile based on the presence or absence of a dominant frequency other than the second frequency based on the depth direction of the wall pile, which is lower than the first frequency based on the width direction of the wall pile, in the spectral analysis." The method further describes "fourier transforming the reflection characteristics in the spectral analysis, removing frequencies at least above the first frequency, generating an inverse Fourier transform waveform, and further evaluating the soundness of the wall pile based on the shape of the inverse Fourier transform waveform at the time when the reflection waveform at the tip of the wall pile appears." [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2014-224756 [Patent Document 2] Japanese Patent Publication No. 2019-32303 [Patent Document 3] Japanese Patent Publication No. 2021-9071 [Patent Document 4] Japanese Patent Publication No. 2019-211308 [Overview of the project] [Problems that the invention aims to solve]

[0009] Up until now, various evaluation methods have been studied, primarily focusing on existing concrete piles. In contrast, the evaluation of steel pipe piles, which are steel pipes with filling material, has not been adequately considered. Unlike concrete piles, steel pipe piles are composed of two or more different materials, including steel pipes and filling material, and a method that can appropriately evaluate their condition is desired.

[0010] This invention aims to address the issues described above, and its objective is to provide a pile evaluation method and evaluation apparatus that can evaluate steel pipe piles embedded in the ground. [Means for solving the problem]

[0011] The present invention relates to a method for evaluating piles embedded in the ground, wherein the pile is a steel pipe pile having two or more members made of different materials, including a steel pipe and a filling material, and the method includes analyzing the time-domain waveforms of incident and reflected waves observed at the pile head as they propagate between the pile head and the pile tip due to impact on the pile head.

[0012] The above evaluation method preferably includes converting the time-domain waveforms of the incident wave and the reflected wave into frequency components using a Fourier transform.

[0013] In this case, it is preferable to include extracting the frequency component due to the reflected wave from the tip of the pile from the frequency component obtained by the Fourier transform.

[0014] Furthermore, in this case, it is preferable to estimate the pile length of the steel pipe pile based on the frequency of the frequency component of the reflected wave from the pile tip and the longitudinal wave propagation velocity of the steel pipe pile.

[0015] The longitudinal wave propagation velocity may be determined based on the material of the steel pipe of the steel pipe pile and / or the material of the filling material.

[0016] The above evaluation method preferably includes determining the period from the frequency of the frequency component of the reflected wave from the pile tip, and estimating the presence or absence of damage between the pile head and the pile tip from the waveform shape in the middle of the period in the time-domain waveform.

[0017] In this case, it is preferable to include estimating the position of the damaged portion based on the period of the frequency component due to the reflected wave from the pile tip, the interval between the observation time of the incident wave and the observation time of the reflected wave from the damaged portion, and the pile length.

[0018] The above evaluation method can include striking the pile head, observing the incident wave and the reflected wave using a sensor attached to the pile head, and acquiring the time-axis waveforms of the incident wave and the reflected wave.

[0019] Here, the sensor is attached to a part of the steel pipe and / or a part of the filling material exposed at the end face of the pile head, and the striking may be applied to the part where the sensor is attached among the part of the steel pipe and the part of the filling material.

[0020] The pile can be a pile work as the object.

[0021] The pile evaluation apparatus of the present invention is an apparatus for evaluating a pile embedded in the ground, which targets a steel pipe pile having members of two or more different materials including a steel pipe and a filling material as the pile, and is provided with a processing unit that analyzes the time-axis waveform observed at the pile head of the incident wave and the reflected wave propagating between the pile head and the pile tip of the pile due to striking on the pile head of the pile.

[0022] It is preferable that the processing unit converts the time-axis waveforms of the incident wave and the reflected wave into frequency components using Fourier transform.

[0023] It is preferable that the processing unit extracts the frequency component due to the reflected wave from the pile tip from the frequency components obtained by the Fourier transform.

[0024] The processing unit can estimate the pile length of the steel pipe pile based on the frequency of the frequency component due to the reflected wave from the pile tip and the longitudinal wave propagation velocity of the steel pipe pile.

[0025] The longitudinal wave propagation velocity may be determined based on the material of the steel pipe of the steel pipe pile and / or the material of the filling material.

[0026] Preferably, the processing unit obtains a period from the frequency of the frequency component due to the reflected wave from the pile tip, and estimates the presence or absence of a damaged portion between the pile head and the pile tip of the pile from the waveform shape in the middle of the period in the time-axis waveform.

[0027] Preferably, the processing unit estimates the position of the damaged portion based on the period of the frequency component due to the reflected wave from the pile tip, the interval between the observation time of the incident wave and the observation time of the reflected wave from the damaged portion, and the pile length.

[0028] The above evaluation apparatus may include a striking unit that applies a strike to the pile head, a sensor attached to the pile head to observe the incident wave and the reflected wave, and an input unit that acquires observation information from the sensor.

[0029] The sensor is used by being attached to a part of the steel pipe and / or a part of the filling material exposed on the end face of the pile head, and may be used to apply the strike to the part where the sensor is attached, among the part of the steel pipe and the part of the filling material.

[0030] The piles may be targeted for pile work. [Effects of the Invention]

[0031] According to the pile evaluation method and evaluation apparatus of the present invention, a steel pipe pile embedded in the ground can be evaluated. [Brief Description of the Drawings]

[0032] [Figure 1] This is a cross-sectional view along the vertical direction, showing an example of a pile that can be targeted by the pile evaluation method according to one embodiment of the present invention. [Figure 2]This is a flowchart showing each step of a pile evaluation method according to one embodiment of the present invention. [Figure 3] This is a block diagram showing a pile evaluation device according to one embodiment of the present invention. [Figure 4] This graph shows an example of a time-domain waveform that can be used for analysis in the pile evaluation method according to one embodiment of this invention. [Figure 5] This is a perspective view showing a specific example of how to strike the pile head. [Figure 6] This graph shows an example of a Fourier spectrum of frequency components obtained by the Fourier transform of a pile evaluation method according to one embodiment of this invention. [Figure 7] This graph shows the normalized time-domain waveforms and Fourier spectra of Examples No. 1 and No. 2. [Figure 8] This graph shows the normalized time-domain waveform and Fourier spectrum for Examples No. 3 and No. 4. [Figure 9] This graph shows the normalized time-domain waveforms and Fourier spectra of Examples No. 5 and No. 6. [Figure 10] This graph shows the normalized time-domain waveform and Fourier spectrum for Examples No. 7 and No. 8. [Modes for carrying out the invention]

[0033] Embodiments of this invention will be described in detail below. A pile evaluation method according to one embodiment of this invention (hereinafter also simply referred to as the "evaluation method") is a method for evaluating piles embedded in the ground, and applies to steel pipe piles having members of two or more different materials, including a steel pipe and a filling material.

[0034] Figure 1 shows, as an example, a steel pipe pile 1 used as a pile (so-called landslide prevention pile, etc.). Here, we will explain in detail using the example of pile construction, but this invention can also be applied to various types of piles other than pile construction, such as existing piles remaining in the ground after the demolition of structures such as buildings, cast-in-place concrete piles immediately after construction, and anchor works.

[0035] In the ground beneath which the illustrated pile 1 is embedded from the ground surface 51 of the slope, if a landslide were to occur, the moving layer 52 on the ground surface 51 side could move downward along the slope relative to the immovable layer 53 along the sliding surface 54, such as an arc shape. To suppress the landslide, the pile 1 may be embedded in the ground until it penetrates the moving layer 52 and the pile tip 3 reaches the immovable layer 53. Such a pile 1 is installed to stabilize the slope by resisting the movement of the moving layer 52 through resistive bending moments, shear resistance forces at the sliding surface 54, etc.

[0036] These landslide prevention piles 1 have been used in large numbers on various slopes for a relatively long time, and from a maintenance perspective, it is important to check for deterioration or damage and evaluate whether they can continue to perform the required function in the future.

[0037] However, since the pile 1 described above is mostly underground, it is difficult to directly observe and evaluate its entirety. On the other hand, the pile head 2 of pile 1 is generally exposed above ground from the ground surface 51 of the slope. Even if the pile head is also buried underground, it is often located closest to the ground surface underground, so it can be easily exposed above ground. Therefore, here, the soundness of pile 1 can be evaluated without pulling out pile 1 by using this exposed pile head 2.

[0038] In the evaluation method according to one embodiment of this invention, steps S1 to S9 illustrated in Figure 2 are performed sequentially. However, as will be described in detail later, some steps (such as steps S1 and S2) may be omitted if time-domain waveforms can be obtained separately.

[0039] The evaluation method shown in Figure 2 can be performed, at least partially (for example, steps S3 to S9) using a pile evaluation device (hereinafter also simply referred to as the "evaluation device"). As shown in Figure 3, the evaluation device may comprise a processing unit for analyzing input information, an input unit for the user to input predetermined information, an output unit for outputting the results of processing in the processing unit, and a storage unit for storing information. The processing unit is configured to transmit and receive information or signals via a bus with the input unit, output unit, and storage unit. The processing unit often includes a processor, RAM (Random Access Memory), and ROM (Read Only Memory), and performs the above processing by executing a program recorded in the ROM or storage unit. The storage unit may consist of an HDD (Hard Disk Drive) or flash memory.

[0040] In step S1 of Figure 2, as shown in Figure 1, the pile head 2 of the pile 1 is struck with the striking part 8, thereby applying a blow to the pile head 2 in the direction in which the pile 1 extends (vertical or up-and-down direction in Figure 1). In the illustrated example, the striking part 8 is represented as a hammer for ease of understanding, but it is not limited to this form as long as it can apply the desired blow to the pile head 2.

[0041] When the pile head 2 is struck, an incident wave is generated at the pile head 2 inside the pile 1. This wave propagates along the direction in which the pile 1 extends towards the pile tip 3, which is located deep underground. When the incident wave strikes some interface, it is reflected, generating a reflected wave that propagates in the opposite direction to the incident wave, towards the pile head 2. When this reflected wave propagates towards the pile tip 3 and strikes an interface such as the pile head 2, further reflected waves may be generated there. It is thought that longitudinal reflected waves are generated at both the pile head 2 and the pile tip 3 with each reflection.

[0042] Regarding the above-mentioned interface, typically the pile tip 3 and the pile head 2 serve as the interface. Furthermore, if there is a damaged area DA in the pile 1, that damaged area DA is also considered to be an interface. With a single blow to the pile head 2, numerous elastic waves, including the incident and reflected waves, propagate within the pile 1.

[0043] In step S2, the incident and reflected waves are observed by a sensor 7, such as an accelerometer, attached to the pile head 2. When using an accelerometer sensor 7, when an incident wave is generated at the pile head 2, or when a reflected wave reaches the pile head 2, the vibrations caused by these incident and reflected waves are measured as acceleration by the sensor 7. As a result, as shown in Figure 4, the time-domain waveforms of the incident and reflected waves observed at the pile head 2 (i.e., the change over time of the measured value at the sensor 7) can be plotted on a graph where the horizontal axis is time and the vertical axis is the measured value.

[0044] The evaluation device may further include, if necessary, a striking unit 8 for striking the pile head 2, and a sensor 7 attached to the pile head 2. The input unit of the evaluation device can receive observational information such as the time-dependent change of measured values ​​or time-domain waveforms from the sensor 7. The processing unit of the evaluation device can use this observational information to analyze the time-domain waveforms of the incident and reflected waves. Alternatively, if the evaluation device does not have a striking unit 8 and a sensor 7, steps S1 and S2 may not be performed, and the input unit may acquire separately obtained measured values ​​or time-domain waveform information, which can then be analyzed by the processing unit.

[0045] Incidentally, the pile 1, as a steel pipe pile, is a composite material composed of two or more different material components. As shown in Figure 5, the components of the pile 1, which is a steel pipe pile, include a steel pipe 4 and filler material 5 and / or 6. More specifically, the pile 1 may have an internal filler material 5 filled inside the steel pipe 4, or a tubular external filler material 6 (so-called grout), such as a circular pipe, provided around the steel pipe 4. The internal filler material 5 may be pre-packed concrete, ready-mixed concrete, mortar, or cement milk. The external filler material 6 may be mortar or cement paste.

[0046] For such a pile 1, analysis may be performed for each component made of a different material. In this case, for each component made of a different material, impact can be applied to the pile head 2 and measurements can be taken by the sensor 7 to generate the respective time-domain waveforms.

[0047] For example, when performing an analysis on the steel pipe 4 of pile 1, in step S1, as shown in Figure 5(a), the striking unit 8 can strike a part of the exposed end face of the steel pipe 4 at the pile head 2. The sensor 7 can also be attached to the exposed part (end face, etc.) of the steel pipe 4 at the pile head 2. As a result, in step S2, the vibrations caused by incident and reflected waves propagating between the pile head 2 and the pile tip 3 in the steel pipe 4 of pile 1 are measured over time by the sensor 7.

[0048] Furthermore, the locations where the striking unit 8 delivers impact and where the sensor 7 is attached may be a part of the end face of the inner filler 5 when analyzing the inner filler 5, and a part of the end face of the outer filler 6 when analyzing the outer filler 6, as shown in Figures 5(b) and (c), respectively. In other words, the locations where the striking unit 8 delivers impact may be the exposed parts of the end face of the steel pipe 4, the exposed parts of the inner filler 5, and the exposed parts of the outer filler 6 where the sensor 7 is attached. If the outer circumferential surface of the steel pipe 4 or outer filler 6 of the pile head 2 is exposed, that outer circumferential surface may be used as the location where the striking unit 8 delivers impact and where the sensor 7 is attached.

[0049] Alternatively, the entire pile 1, which consists of a steel pipe 4, an inner filling material 5, and / or an outer filling material 6, may be considered as a single unit, and the analysis may be performed on the entire pile 1.

[0050] If necessary, in step S3, the time-domain waveforms of the incident and reflected waves can be normalized by dividing them by the maximum acceleration of the incident wave. Alternatively, the time-domain waveform may be divided not only by the incident wave, but also by the maximum acceleration of either the incident or reflected wave (for example, the acceleration of the first reflected wave). Such normalization makes the vertical axis value of the time-domain waveform constant regardless of the magnitude of the impact delivered to the pile head 2, making comparison and analysis easier. However, this normalization step S3 may be omitted.

[0051] Next, in step S4, the normalized time-domain waveforms of the incident and reflected waves can be converted into frequency components by Fourier transform. This decomposes the time-domain waveform resulting from the combined wave of the incident and reflected waves into multiple frequency components, allowing us to determine the frequency and amplitude or magnitude of each individual wave of the incident and reflected waves. The frequency components converted by the Fourier transform can be represented as a so-called Fourier spectrum on a graph with frequency on the horizontal axis and magnitude on the vertical axis, as shown in Figure 6.

[0052] While it is possible to use the Discrete Fourier Transform (DFT) here, it is preferable to use the Fast Fourier Transform (FFT). Using the Fast Fourier Transform reduces the overall computational load and alleviates the load on the system. In cases where the amount of data is large, the Discrete Fourier Transform may be preferable.

[0053] The frequency components obtained from the Fourier transform in step S4 may be normalized in step S5 if necessary. When performing a Fourier transform, the amplitude spectrum values ​​may change depending on the number of data points. In step 4, for example, dividing the amplitude spectrum by half the number of data points allows for comparison of results with different numbers of data points. In some cases, step S4 may be omitted.

[0054] In step S6, the frequency component due to the reflected wave from the pile tip 3 is extracted from the frequency components obtained by the Fourier transform. The reflected wave from the pile tip 3 takes longer to reach the pile head 2 than the reflected wave from the damaged area DA, and in many cases, it can become the waveform with the longest period on the time axis. For this reason, as shown in Figure 6, the frequency component FE1 with the smallest frequency among the frequency components obtained by the Fourier transform can be extracted as the frequency component due to the reflected wave from the pile tip 3. Here, as an example, the frequency component due to the reflected wave from the pile tip 3 is also described using the same symbol "FE1" as the frequency component FE1 with the smallest frequency.

[0055] In step S7, the pile length Lp is estimated from the frequency f1 of the frequency component FE1 due to the reflected wave from the pile tip 3, and the longitudinal wave propagation velocity v of the steel pipe pile. Since frequency is the reciprocal of period, the period T1 of the frequency component FE1 due to the reflected wave from the pile tip 3 can be obtained from the following equation: T1[s]=1 / f1[Hz]. Furthermore, the period T1 of the frequency component FE1 corresponds to twice the time required for the reflected wave to propagate in one direction from the pile tip 3 to the pile head 2. Therefore, the pile length Lp can be calculated from the following equation: Lp[m]=v[m / s]×T1[s] / 2=v[m / s] / (f1[Hz]×2).

[0056] Here, the longitudinal wave propagation velocity v of the steel pipe pile can be determined based on the material of the steel pipe 4 and / or the material of the filler material 5 and / or 6. When performing analysis for members made of different materials, the longitudinal wave propagation velocity of the material of the member being analyzed (steel pipe 4, inner filler material 5, or outer filler material 6) is used as the longitudinal wave propagation velocity v in the above formula. The individual longitudinal wave propagation velocities of the steel pipe, inner filler material, outer filler material (mortar, concrete, etc.) are known. For example, a longitudinal wave propagation velocity of 5120 m / s may be used for the steel pipe, and a longitudinal wave propagation velocity of 3800 m / s to 4000 m / s may be used for the cast-in-place concrete pile. The longitudinal wave propagation velocity may be a value within the range of 3500 m / s to 5120 m / s, particularly 4500 m / s to 5120 m / s. Alternatively, the longitudinal wave propagation velocity v may be the longitudinal wave propagation velocity of the entire pile 1, which is a composite material including the steel pipe 4, the inner filler 5, and / or the outer filler 6. In this case, it is conceivable to conduct tests on the same type of composite material in advance to determine the longitudinal wave propagation velocity of the composite material, or to multiply the ratio of each material at the end face of the pile head 2 by the longitudinal wave propagation velocity of each material and add them together.

[0057] In step S8, we estimate whether or not there is damage between the pile head 2 and the pile tip 3 of pile 1. First, as mentioned earlier, we determine the period T1 from the frequency f1 of the frequency component FE1 due to the reflected wave from the pile tip 3 using the following equation: T1[s]=1 / f1[Hz].

[0058] In the time-domain waveform graph shown in Figure 4, the earliest peak Pa represents the acceleration when the incident wave is generated at the pile head 2, and the peak Pb that appears after a period T1 has elapsed from peak Pa is considered to be the acceleration when the reflected wave from the incident wave at the pile tip 3 reaches the pile head 2. In the example shown in Figure 4, a peak Pc appears midway through the period T1 between peak Pa and peak Pb, separate from peaks Pa and Pb. This peak Pc is considered to be the result of the incident wave generated at the pile head 2 being reflected before reaching the pile tip 3, and the resulting reflected wave propagating back to the pile head 2. A possible interface from which the incident wave can be reflected before reaching the pile tip 3 is the damaged area DA. Therefore, if a peak Pc appears midway through the period T1, it can be inferred that a damaged area DA exists. In this way, the presence or absence of a damaged area DA between the pile head 2 and the pile tip 3 of pile 1 can be estimated from the waveform shape midway through the period T1 in the time-domain waveform.

[0059] As described above, if a damaged area DA is estimated in step S8, the location of that damaged area DA can also be estimated in step S9. This estimation uses the period T1 of the frequency component of the reflected wave from the pile tip 3, the interval between the observation time of the incident wave and the observation time of the reflected wave from the damaged area DA, and the pile length Lp mentioned earlier.

[0060] More specifically, from the time-domain waveform shown in Figure 4, we can determine the interval Td between the observation time of the incident wave and the observation time of the reflected wave from the damaged area DA. Therefore, the distance Dd from the pile head 2 to the damaged area DA, which represents the position of the damaged area DA, can be calculated using the following equation: Dd[m]=Lp[m]×Td[s] / T1. [Examples]

[0061] Next, we will describe the results of a trial implementation of the pile evaluation method of this invention, confirming its effectiveness. However, this description is for illustrative purposes only and is not intended to be limiting.

[0062] As shown in Table 1, tests were conducted on each of the eight steel pipe piles that simulated steel pipe piles. Each pile differed from the others in terms of pile length, presence or absence of internal filling material, and presence, location, and extent of cross-sectional defects simulating damaged areas. In Nos. 4 to 6, cross-sectional defects were formed in the 1 / 4, 2 / 4, or 3 / 4 regions of the entire circumference, respectively.

[0063] [Table 1]

[0064] In the test, a pile was placed on a stand, and an accelerometer was attached to the pile head. The pile head was then struck, and the acceleration of the vibration caused by the elastic wave generated in the pile was measured by the accelerometer at the pile head. The time-domain waveforms obtained from these measurements were then analyzed according to steps S3 to S5 in Figure 2. The normalized time-domain waveforms and normalized Fourier spectra for No. 1 to No. 8 are shown in Figures 7 to 10.

[0065] In the graphs No. 1 to No. 8 shown in Figures 7 to 10, the frequency component with the lowest frequency among the frequency components of the Fourier spectrum is considered to be due to the reflected wave from the pile tip. The frequency and period of this frequency component are shown in the same figure, and if the longitudinal wave propagation velocity is also known, the pile length can be estimated using these values.

[0066] Furthermore, since the pile length is known in this test, the longitudinal wave propagation velocity can be determined. The longitudinal wave propagation velocity of the steel pipe pile used here is estimated to be approximately 5120 m / s. Also, comparing No. 3 to No. 6 in Figures 8 and 9, it can be seen that the longitudinal wave propagation velocity of the steel pipe is constant regardless of the presence or size of the cross-sectional defect.

[0067] In the time-domain waveforms of No. 3 to No. 6 shown in Figures 8 and 9, a peak appears in the time-domain waveforms of No. 5 and No. 6 between the time when the incident wave, which is the earliest peak, was observed and the time when the reflected wave from the pile tip was observed, after the period of the above frequency components (2.34 ms) has elapsed (1.56 ms after the observation time of the incident wave). This peak is considered to be due to the reflected wave from the cross-sectional defect. Therefore, it can be said that the presence or absence of damage can be estimated from the waveform shape in the middle of the time-domain waveform period. However, in No. 4, as shown in Figure 8, no such peak appears in the time-domain waveform. This is thought to be due to the small cross-sectional defect.

[0068] Comparing No. 2 and No. 7, it is estimated that in No. 7, the longitudinal wave propagation velocity decreases to approximately 4800 m / s due to the addition of an internal mortar filler (see Figures 7 and 10).

[0069] Based on the above, it is suggested that this invention may allow for the evaluation of steel pipe piles embedded in the ground. [Explanation of Symbols]

[0070] 1 stake 2 Pile head 3 Pile tip 4 Steel pipe 5 Inner filling material (filling material) 6 Outer filling material (filling material) 7 Sensors 8. Hitting section 51 Ground surface 52 Moving Layer 53 Unmovable layer 54 Slip surface Lp pile length DA damaged area Dd is the distance from the pile head to the damaged area. S1-S9 Steps Pa, Pb, Pc peaks on the time-domain waveform FE1: The lowest frequency component f1 is the frequency of the lowest frequency component. T1: Period of the lowest frequency component. Td is the interval between the observation time of the incident wave and the observation time of the reflected wave from the damaged area.

Claims

1. A method for evaluating piles embedded in the ground, The aforementioned piles include steel pipe piles having members made of two or more different materials, including steel pipes and filling materials. A method for evaluating a pile, comprising analyzing the time-domain waveforms of incident and reflected waves observed at the pile head as they propagate between the pile head and the pile tip due to impact on the pile head.

2. The method for evaluating a pile according to claim 1, comprising converting the time-domain waveforms of the incident wave and the reflected wave into frequency components using a Fourier transform.

3. The method for evaluating a pile according to claim 2, further comprising extracting frequency components due to reflected waves from the pile tip from the frequency components obtained by the Fourier transform.

4. A method for evaluating a pile according to claim 3, comprising estimating the pile length of the steel pipe pile based on the frequency of the frequency component of the reflected wave from the tip of the pile and the longitudinal wave propagation velocity of the steel pipe pile.

5. The method for evaluating a pile according to claim 4, wherein the longitudinal wave propagation velocity is determined based on the material of the steel pipe and / or the material of the filling material of the steel pipe pile.

6. The period is determined from the frequency of the frequency component of the frequency wave reflected from the tip of the pile, and The presence or absence of damage between the pile head and the pile tip is estimated from the waveform shape during the period in the time-axis waveform. The method for evaluating piles according to claim 4, including the method described in claim 4.

7. A method for evaluating a pile according to claim 6, comprising estimating the location of the damaged portion based on the period of the frequency component of the reflected wave from the tip of the pile, the interval between the observation time of the incident wave and the observation time of the reflected wave from the damaged portion, and the length of the pile.

8. A method for evaluating a pile according to claim 1, comprising striking the pile head, observing the incident wave and the reflected wave using a sensor attached to the pile head, and obtaining the time-domain waveforms of the incident wave and the reflected wave.

9. The sensor is attached to a part of the steel pipe and / or a part of the filling material that is exposed on the end face of the pile head. The method for evaluating a pile according to claim 8, wherein the impact is applied to the portion of the steel pipe and the portion of the filler material to which the sensor is attached.

10. The method for evaluating piles according to claim 1, wherein the piles are pile works.

11. A device for evaluating piles embedded in the ground, The aforementioned piles include steel pipe piles having members made of two or more different materials, including steel pipes and filling materials. A pile evaluation device comprising a processing unit for analyzing the time-domain waveforms observed at the pile head of incident and reflected waves propagating between the pile head and the pile tip of the pile due to impact on the pile head of the pile.

12. The pile evaluation apparatus according to claim 11, wherein the processing unit converts the time-domain waveforms of the incident wave and the reflected wave into frequency components using a Fourier transform.

13. The pile evaluation apparatus according to claim 12, wherein the processing unit extracts the frequency component due to the reflected wave from the pile tip from the frequency component obtained by the Fourier transform.

14. The pile evaluation device according to claim 13, wherein the processing unit estimates the pile length of the steel pipe pile based on the frequency of the frequency component of the reflected wave from the pile tip and the longitudinal wave propagation velocity of the steel pipe pile.

15. The pile evaluation device according to claim 14, wherein the longitudinal wave propagation velocity is determined based on the material of the steel pipe and / or the material of the filling material of the steel pipe pile.

16. The aforementioned processing unit, From the frequency of the frequency component of the reflected wave from the tip of the pile, the period is determined. The pile evaluation device according to claim 14, which estimates the presence or absence of damage between the pile head and the pile tip of the pile from the waveform shape in the middle of the period in the time-axis waveform.

17. The pile evaluation device according to claim 16, wherein the processing unit estimates the position of the damaged portion based on the period of the frequency component of the reflected wave from the tip of the pile, the interval between the observation time of the incident wave and the observation time of the reflected wave from the damaged portion, and the pile length.

18. The pile evaluation device according to claim 11, comprising: a striking unit that strikes the pile head; a sensor attached to the pile head for observing the incident wave and the reflected wave; and an input unit for acquiring observation information from the sensor.

19. The sensor is used by being attached to a part of the steel pipe and / or a part of the filling material that is exposed on the end face of the pile head. The pile evaluation device according to claim 18, which is used to apply the aforementioned impact to the portion of the steel pipe and the portion of the filling material to which the sensor is attached.

20. The pile evaluation device according to claim 11, wherein the pile refers to a pile construction.

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