JP2006038598A - Inspection method for buried pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To precisely inspect a deterioration degree in a buried pipe such as a buried pipe and a ceramic pipe constituting a sewer pipe line, an agricultural water pipe line or the like. <P>SOLUTION: A correlation between a parameter obtained from a force-deformation relation (for example, load-displacement curve) for indicating force applied from an outside onto a tested pipe and a deformation of the tested pipe generated thereby, and an impact elastic wave test data (for example, low-frequency area ratio in a spectral distribution) obtained by carrying out an impact elastic wave test for the tested pipe is found preliminarily, an impact elastic wave measured data of the inspection objective pipe is collected by carrying out the impact elastic wave test for the tested pipe, the observed impact elastic wave measured data is evaluated on the basis of the correlation between the parameter obtained from the force-deformation relation and the impact elastic wave test data, so as to grasp the deterioration degree in the inspection objective pipe. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a buried pipe inspection method for inspecting a deterioration state of a buried pipe.

  In sewage pipes and agricultural water pipes, accidents such as depressions and water leakage are increasing due to corrosive wear and breakage of buried pipes over time. For this reason, appropriate repair and renewal based on the appropriate deterioration degree diagnosis and the survey results are desired.

  In the diagnosis survey of sewage pipelines and agricultural water pipelines, in general, in order to determine the order of repair and reconstruction work and the construction method, ranking of the degree of deterioration between the element areas constituting the survey basin, and quantitative It is necessary to grasp the progress of the deterioration level.

  For this reason, conventionally, a method is generally used in which an appearance inspection is performed using visual observation or a TV camera, and a physical property is investigated by removing the core if necessary. However, with such a method, only visible deterioration can be detected, and deterioration on the outer periphery and inside of the pipe is overlooked, and it is difficult to appropriately and quantitatively grasp the deterioration phenomenon. In addition, in order to collect quantitative data, it is necessary to remove a large amount of cores, and there is a disadvantage that the strength of the sewage pipe and the agricultural water pipe is impaired and work is troublesome.

On the other hand, application of inspection methods performed on concrete structures is also considered. For example, systems for predicting crack width and depth using elastic waves have been proposed (see, for example, Patent Document 1 and Patent Document 2). However, according to this inspection system, the propagation energy of elastic waves and the decrease in the number of elastic wave counts (the number of counts with a predetermined amplitude or more) are used, so the influence of the surrounding situation where the buried pipe is buried. There is a problem that the inspection accuracy is poor.
JP-A-10-142200 JP 09-269215 A

  The present invention has been made to solve the above problems, and the degree of deterioration of buried pipes that construct sewage pipes, agricultural water pipes, etc. can be determined with high accuracy without being affected by the buried environment. It aims at providing the inspection method of the buried pipe which can be inspected.

  The inspection method of the present invention is a method for inspecting the deterioration state of an embedded pipe from the inside of the pipe, and is obtained from a force-deformation relationship indicating a relation between an external force applied to the test pipe and a deformation of the test pipe generated thereby. And a shock elastic wave test data obtained by performing a shock elastic wave test on the test tube in advance, and performing a shock elastic wave test on the inspection target tube, Shock elastic wave measurement data is collected, and the actually measured shock elastic wave measurement data is evaluated based on the correlation between the parameters obtained from the force-deformation relationship and the shock elastic wave test data, and It is characterized by quantitatively determining the degree of deterioration.

  In the present invention, a load-displacement curve or a stress-strain curve may be used as a parameter obtained from the force-deformation relationship of the test tube.

  Further, as a parameter obtained from the force-deformation relationship, the angle ratio of the slope of the load-displacement curve or stress-strain curve may be used.

  In the present invention, as the shock elastic wave test data and the actually measured shock elastic wave data, a shock elastic wave test is performed to measure a propagation wave of the tube, a frequency spectrum is analyzed for the propagation wave, and a constant in the frequency spectrum is analyzed. It is preferable to use the area ratio of the low frequency component to the frequency region.

  The present invention is described in detail below.

  First, when cracks occur in a tubular body such as a reinforced concrete pipe, the rigidity decreases. As a method for evaluating the rigidity of the tubular body, a method for measuring a force-deformation curve such as a load-displacement curve (or stress-strain curve) is generally known. Another method is an impact vibration test. And in this invention, it discovered that there existed a correlation between the measurement result of such a force-deformation curve and a shock elastic wave test (it mentions later for details), As mentioned above, force-deformation Correlation between the curve and the test data of the shock elastic wave test is obtained in advance, and the measured shock elastic wave measurement data when the shock elastic wave test of the pipe to be inspected (existing buried pipe) is performed is the force − It is characterized by quantitatively grasping the degree of deterioration of the pipe to be inspected by evaluating based on the correlation between the deformation curve and the test data of the shock elastic wave test.

  Here, in the present invention, as a specific test method for obtaining the correlation between the force-deformation curve and the test data of the shock elastic wave test, for example, displacement (or strain) generated by applying a linear load to the tube In the loading test to obtain a load-displacement curve (or stress-strain curve) and the load-displacement measurement process, the line load on the tube is unloaded at every predetermined step, and the following impact elastic wave The method of conducting the test is adopted.

-Shock elastic wave test-
In the present invention, the shock elastic wave test performed on the test tube and the test target tube is performed as follows.

[input method]
As the input device, a hammer, a steel ball or an impulse hammer can be used, but it is desirable to always apply the hammer with the same force. For example, a hammer with a constant force using a Schmitt hammer, spring, piston, etc. A method of launching a steel ball or the like, or a method of dropping a steel ball or the like from a certain height is desirable. When an impulse hammer is used, it is desirable to measure numerical data of input information so that it can be reflected during analysis.

  In particular, as an input device for evaluating the intensity of the maximum peak, it is desirable to use a striking tool that can digitize input information such as an impulse hammer or a striking tool that can perform striking with a constant force. .

[Reception method]
As the receiver, an acceleration sensor, an AE sensor, a vibration sensor, or the like can be used. As a method for setting the receiver, the receiver may be fixed with a tape, an adhesive, or the like, or may be crimped using a hand or a holding jig.

  Since these input devices and receiving devices may come into contact with water, acidic water, or basic water, it is desirable that the input device and the receiving device be formed of a material having excellent corrosion resistance such as stainless steel.

[Measurement method]
An elastic wave is input to the inner surface of the tube with an impulse hammer or the like. On the other hand, a propagation wave propagated through the tube is measured by a receiver set in the tube, and a waveform is stored by a recording device (measurement of received data). It is desirable that the incident position and the receiver position be separated from each other by 1/4 or more of the tube length of the inspection target tube. This is because changes in the vibration phenomenon of the entire tube due to deterioration such as cracks are easily captured. Further, it is desirable that the incident position and the receiving position are installed so that the relative positions are the same.

[Calculation of low frequency area ratio]
As a calculation method, for example, there are the following two methods.

  (1) Perform FFT on the measured waveform data and draw a frequency spectrum. In this frequency spectrum distribution, the area ratio of low frequency components to a certain frequency interval (low frequency area ratio = [area of low frequency components (eg, 0 to 5 kHz)] / [area of constant interval components (eg, 0 to 10 kHz)]. Ask for.

  (2) For the measured input and received data, draw a frequency spectrum that takes into account the relationship between the input (striking side) and the output (receiving side). In this frequency spectrum distribution, the area ratio of low frequency components to a certain frequency interval (low frequency area ratio = [area of low frequency components (eg, 0 to 5 kHz)] / [area of constant interval components (eg, 0 to 10 kHz)]. When the analysis method of (2) is adopted, it is necessary to digitize the impact force (input information) of the impulse hammer, where the frequency spectrum considering the relationship between input and output is For example, if the input Fourier spectrum is A (f), the output Fourier spectrum is B (f), and the transfer function (frequency response function) is H (f), then H (f) = B (f) / A (f ), And this H (f) is drawn as the distribution of the frequency spectrum here.

  In the present invention, the correlation between the load-displacement curve obtained in the above loading test and the low frequency area ratio obtained in the shock elastic wave test is obtained, for example, [low frequency area as shown in FIG. Ratio]-[angle ratio of inclination in load-displacement curve] (details will be described later). As shown in FIG. 8, the [low frequency area ratio] and the [inclination angle ratio in the load-displacement curve] are in a proportional relationship (linear relationship). Conduct a wave test to obtain the above-mentioned low frequency area ratio, and evaluate the actually measured low frequency area ratio based on the relationship of [low frequency area ratio]-[inclination angle ratio in load-displacement curve]. Can quantitatively grasp the deterioration degree (destructive state) of the inspection target pipe.

  The test data of the shock elastic wave test used in the present invention includes the low frequency area ratio, resonance frequency ratio, received waveform amplitude value, received waveform energy, peak frequency, frequency center of gravity, or waveform decay time. May be.

  Here, examples of the buried pipe to which the inspection method of the present invention is applied include a concrete pipe, a reinforced concrete pipe, a ceramic pipe, a metal pipe, a resin pipe, or an FRPM pipe (composite pipe of mortar and FRP). Examples of the cross-sectional shape of the buried pipe include a circular shape, an oval shape, a rectangular shape, and a horseshoe shape.

  According to the buried pipe inspection method of the present invention, a parameter obtained from a force-deformation relationship indicating a relation between an external force applied to the test tube and a deformation of the test tube generated thereby, and a shock elastic wave is applied to the test tube. The correlation with the shock elastic wave test data obtained by performing the test is obtained in advance, the shock elastic wave test is performed on the inspection target pipe (buried pipe), and the shock elastic wave measurement data of the inspection target pipe is obtained. Since the impact elastic wave measurement data collected and evaluated is evaluated based on the correlation between the parameter obtained from the force-deformation relationship and the shock elastic wave test data, the deterioration state of the inspection target pipe is inspected. The degree of deterioration can be determined quantitatively with high accuracy without being affected by the surrounding situation where the inspection symmetric pipe is buried, and thereby the method and priority of reconstruction and repair can be determined.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Example 1>
First, the test tube and each test method used in this example will be described.

−Test tube−
A concrete fume pipe (product made by Nippon Fume Pipe Co., Ltd.) having a nominal diameter of 250 mm (pipe length: 2 m) based on JIS A 5372 B type 1 type standard was used.

-Loading test by external load (external pressure test)-
As shown in FIGS. 1A and 1B, a line load 1 having a shape extending along the axial direction of the test tube P was loaded onto the test tube P from above. In addition, as shown in FIG. 2, a high-sensitivity displacement meter 2 is arranged inside the test tube P along the vertical direction, and the displacement of the test tube P when a line load 1 is applied to the test tube P is measured. Thus, a load-displacement curve was obtained.

  Here, the loading of the line load 1 is not performed continuously, but the loading of the line load 1 is performed intermittently by unloading the line load 1 (see FIG. 1B) at every predetermined step. . Specifically, after loading of line load 1 is started, unloading is performed once in the elastic region until cracking occurs, the impact acoustic wave test described below is performed, reloading is performed, and then cracking is performed. Unloading was performed at the time of occurrence, and after the impact elastic wave test was carried out, reloading was performed. And after a crack generate | occur | produces, the displacement measured with the high sensitivity displacement meter 2 is [displacement = 2.4mm], [displacement = 4.3mm], [displacement = 6.3], [displacement = 9. 4 ”,“ displacement = 12.6 ”, and“ displacement = 20.3 ”, respectively, the line load 1 was unloaded and the following impact elastic wave test was performed, and then reloaded. .

-Shock elastic wave test-
In this example, the shock elastic wave test was performed as follows.

[Incoming and receiving position]
The incident device and the receiving device are arranged at the positions shown in FIG. 3 to receive the elastic wave and receive the propagation wave.

[Used equipment]
Incident device: Impulse hammer Receiver: Vibration sensor GH-313A (manufactured by Keyence) was used by screwing a cylindrical object having a diameter of 10 mm and a height of 15 mm. The receiver was set by pressing it by hand.

Receiver amplifier: Keyence GA-245
Data logger (recording device): NR-2000 manufactured by Keyence
[Calculation of frequency area]
The input Fourier spectrum A (f) is obtained from the impact force of the incident device (impulse hammer), and the output Fourier spectrum B (f) is obtained from the waveform data of the propagation wave received and recorded by the receiver, and the input Fourier spectrum is obtained. Using the spectrum A (f) and the output Fourier spectrum B (f), the transfer function (frequency response function) H (f) (H (f) = B (f) / A (f) between the input and the output ) And a frequency spectrum taking into account the relationship between input and output was drawn for each measurement point. These frequency spectrum distributions are shown in FIGS. 4 (a) to 4 (c) and FIGS. 5 (a) to 5 (f).

  Next, the frequency region from 0 to 5 kHz and the frequency region from 0 to 10 kHz of the frequency spectrum distribution obtained at each measurement point are obtained, and the low frequency area ratio is calculated by the following formula using them. did. The relationship between the calculated low frequency area ratio and the measurement results at each measurement point of the loading test is shown in Table 1 below and FIG.

  Low frequency area ratio = [area of low frequency component (0 to 5 kHz)] / [area of constant interval component (0 to 10 kHz)]

-Correlation between frequency area and load-displacement curve-
First, as described above, as a factor of the frequency spectrum obtained in the shock elastic wave test, the low frequency area ratio (= [area of low frequency component (0 to 5 kHz)] / [constant interval component (0 to 10 kHz)) Area] is used.

  The factor used in the load-displacement curve is the angle of inclination (apparent stiffness) at each measurement point in the load-displacement curve. In this example, the slope at each measurement point in the load-displacement curve is Use angle ratio.

  Here, the inclination angle ratio at each measurement point in the load-displacement curve is defined as [inclination angle at the measurement point] / [inclination angle at the crack generation point]. The inclination angle at the measurement point refers to the inclination angle of a straight line drawn at each measurement point in the load-displacement curve shown in FIG.

  Then, the results at each measurement point are plotted with the low frequency area ratio of the frequency spectrum distribution obtained as described above as the horizontal axis and the angle ratio of the inclination at each measurement point in the load-displacement curve as the vertical axis. As shown in FIG. 8, it was found that the frequency area ratio and the angle ratio of the inclination at each measurement point in the load-displacement curve are in a proportional relationship (linear relationship). The slope of the graph in FIG. 1 is y = −3.89x + 2.19. Here, x: frequency area ratio, y: angle ratio of inclination at each measurement point in the load-displacement curve.

  Further, when the frequency area ratio = 0.31 at the time of occurrence of cracking is 100%, the frequency area ratio at the maximum load = 0.41 is 0%, and the deterioration progress state of the tubular body is expressed by the residual strength rate, A = −1000x + 410. Where x: frequency area ratio, A: residual intensity ratio (%)).

  From the above, the low frequency area ratio obtained by the shock elastic wave test and the state (residual strength ratio) of the tubular body can be related. Therefore, for the pipe to be inspected (buried pipe), the low frequency area ratio is obtained from the frequency spectrum distribution obtained by carrying out the shock elastic wave test, and the actually measured low frequency area ratio (x) is used as the residual strength described above. By converting the residual strength rate (%) using the estimation function (A = −1000 × + 410), it is possible to grasp the degree of deterioration of the inspection target pipe by a numerical value. As a result, it is possible to determine the method / priority of renovation / repair.

-Judgment process of the degree of deterioration-
A specific example of the deterioration degree determination process will be described with reference to the flowchart shown in FIG. In this example, the determination is performed using FIG. 8, Table 1 and the remaining strength estimation function (A = −1000x + 410).

  Step S1: The propagation wave of the inspection target tube is measured by the measurement method of the shock elastic wave test described above. Note that the measurement conditions and the like are the same as those of the test tube P described above.

  Step S2: FFT is performed on the measured waveform data to calculate a frequency spectrum distribution. Note that the frequency spectrum distribution calculation method is the same as that for the test tube P described above.

  Step S3: A frequency region from 0 to 5 kHz and a frequency region from 0 to 10 kHz of the frequency spectrum distribution are obtained from the frequency spectrum distribution calculated in Step 2, and a low frequency area ratio (= [low Frequency area (0 to 5 kHz)] / [area of constant interval component (0 to 10 kHz)] is calculated.

  Step S4: It is determined whether or not the low frequency area ratio calculated in Step S3 is 0.31 or less (≦ 0.31). If the low frequency area ratio is 0.31 or less, sound (residual intensity ratio) = 100%) (step S7). On the other hand, if the low frequency area ratio exceeds 0.31, the process proceeds to step S5.

  Step S5: If the low frequency area ratio is 0.31 <[low frequency area ratio] ≦ 0.41, it is determined that a crack has occurred (step S8), and the residual strength estimation function (A = −) 1000 × + 410) to calculate the residual strength rate A (%) (steps S9 and S10). On the other hand, when the low-frequency area ratio exceeds 0.41 (0.41 <[low-frequency area ratio]), it is determined as destruction (residual strength = 0%) (step S6).

  As described above, in this example, the state of the inspection target pipe (buried pipe) can be determined by a percentage value, so that the degree of deterioration of the inspection target pipe can be accurately grasped. As a result, for example, when a crack has occurred in the pipe to be inspected, it is possible to grasp the progress of strength deterioration due to the crack with a numerical value (%). Judgment criteria when doing this are clear.

  In the above example, a high-sensitivity displacement meter is placed on the test tube to draw a load-displacement curve. However, the present invention is not limited to this, and a stress-strain curve is obtained by attaching a strain gauge to the test tube. You may make it draw, and you may make it draw the force-deformation curve of a test tube in another external pressure test.

  Further, in the above embodiment, the frequency area ratio is adopted as the test data of the shock elastic wave test. However, the present invention is not limited to this, and the resonance frequency, the received waveform amplitude value, the received waveform energy, the peak frequency, and the frequency are used. Test data such as the center of gravity or waveform decay time may be employed.

  The inspection method of the present invention accurately grasps the degree of deterioration between the elemental areas constituting the survey basin when determining the order and method of repair and renovation work in buried pipes such as sewer pipes and agricultural water pipes. It can be used effectively to do.

It is explanatory drawing of the loading test method implemented by this invention. It is a figure which shows arrangement | positioning of the highly sensitive displacement meter to a test tube. It is a figure which shows arrangement | positioning of the measurement apparatus to the pipe body at the time of performing a shock elastic wave test. It is a figure which shows frequency spectrum distribution based on the waveform data of the propagation wave measured at each measurement point in the loading measurement process. It is a figure which similarly shows frequency spectrum distribution. It is a graph which shows the relationship between the measurement result in each measurement point of a loading test, and a low frequency area ratio. It is a figure which shows a load-displacement curve. It is a graph which shows the relationship between the low frequency area ratio and the angle ratio of the inclination in each measurement point in a load-displacement curve. It is a flowchart which shows an example of the determination process of a deterioration degree.

Explanation of symbols

P Test tube 1 Line load 2 High sensitivity displacement meter

Claims (4)

  A method for inspecting a deterioration state of a buried pipe from the inside of the pipe, the parameter obtained from a force-deformation relation indicating a relation between an external force applied to the test pipe and a deformation of the test pipe generated thereby, and the test pipe Obtain a correlation with shock elastic wave test data obtained by performing a shock elastic wave test on the tube, collect the shock elastic wave measurement data of the inspection target tube by performing a shock elastic wave test on the inspection target tube The measured impact elastic wave measurement data is evaluated based on the correlation between the parameter obtained from the force-deformation relationship and the impact elastic wave test data, and the degree of deterioration of the inspection target tube is quantitatively determined. A method for inspecting buried pipes.   2. The buried pipe inspection method according to claim 1, wherein a load-displacement curve or a stress-strain curve is used as the force-deformation relationship of the test tube.   The buried pipe inspection method according to claim 1, wherein an angle ratio of a slope of a load-displacement curve or a stress-strain curve is used as a parameter obtained from a force-deformation relationship.   As the shock elastic wave test data and the measured shock elastic wave data, a shock elastic wave test is performed to measure the propagation wave of the tubular body, the frequency spectrum is analyzed for the propagation wave, and a certain frequency region in the frequency spectrum is analyzed. 2. The buried pipe inspection method according to claim 1, wherein an area ratio of low frequency components is used.