JP2013231698A - Cavity thickness estimation method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cavity thickness estimation method and device that can nondestructively and easily evaluate the thickness of a cavity present locally on a road.SOLUTION: A plurality of electromagnetic waves W1 differing in frequency band are radiated to a cavity predicted position I of a road 12. Reflected waves W2 of the radiated electromagnetic waves W1 are detected respectively. A position of a start point and a position of an end point of a cavity 13 in the thickness direction are estimated based upon differences of the reflected waves W2 corresponding to differences of the frequency bands of the electromagnetic waves W1. A cavity thickness T is estimated based upon the position of the start point and the position of the end point which are estimated. Consequently, the thickness of the cavity 13 present locally on the road 12 can be easily evaluated without breaking the road 12.

Description

  The present invention relates to a cavity thickness estimation method and apparatus for estimating a cavity thickness of an inspection object.

  In general, for evaluating the thickness of a cavity in an inspection object such as a road, tunnel, retaining wall, revetment, or building, an electromagnetic ground penetrating radar device is moved by an exploration vehicle or human power. Thus, the reflected wave of the electromagnetic wave radiated toward the inspection object is detected, and the detection wave is analyzed to perform nondestructive.

  However, such an evaluation is possible when the cavities are continuous with a certain length, for example, the cavities present at the back of the tunnel, but locally, such as cavities under paved roads. For existing cavities, it is only possible to measure the planar spread, and it is not easy to evaluate the thickness because the amount of information with respect to the movement distance of the underground radar apparatus is small. Therefore, generally, a method is used in which the state inside the cavity is visually confirmed by boring the target object at the predicted cavity position detected by the ground penetrating radar device (see, for example, Patent Document 1). .

Japanese Patent Laid-Open No. 5-87945 (page 3-5, FIG. 1-8)

  However, in the case of the method as described above, it is necessary to drill a hole in the inspection object as a result, so that a part of the inspection object is destroyed and work such as backfilling is required. At the same time, there is a concern that existing buried structures such as pipes and cables may be damaged, and there is a problem that the work becomes large and complicated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a cavity thickness estimation method and apparatus capable of easily evaluating the thickness of a cavity locally present in an inspection object in a nondestructive manner. To do.

  The cavity thickness estimation method according to claim 1 is a cavity thickness estimation method for estimating a cavity thickness of an inspection object, and radiates detection waves of a plurality of different frequency bands at least with respect to a cavity expected position of the inspection object. Then, the reflected waves of these detected waves are detected, respectively, and the positions of the start end and the end of the cavity in the thickness direction are estimated based on the difference in the reflected waves corresponding to the difference in the frequency band of the detected waves. The cavity thickness is estimated based on the estimated start position and end position.

  The cavity thickness estimation method according to claim 2 is the cavity thickness estimation method according to claim 1, wherein at least the detection wave of a plurality of frequency bands having different maximum frequencies from each other is estimated at least with respect to the expected cavity position of the inspection object. Radiation is performed while sweeping from the minimum frequency to the maximum frequency of the frequency band, and the reflected waves of these detected waves are detected, respectively. The position of the start end and the end position in the thickness direction are estimated.

  The cavity thickness estimation method according to claim 3 is the cavity thickness estimation method according to claim 1 or 2, wherein the detection waves are detection waves in a plurality of frequency bands having discontinuous maximum frequencies, and each of the detection waves The reflected wave corresponding to is interpolated between frequency bands.

  According to a fourth aspect of the present invention, there is provided a cavity thickness estimation method according to any one of the first to third aspects, wherein the detection wave is emitted in a state where the cavity is stopped at least at a predicted cavity position of the inspection object. .

  The cavity thickness estimation apparatus according to claim 5 is a cavity thickness estimation apparatus for estimating a cavity thickness of an inspection object, and radiates detection waves in a plurality of different frequency bands at least with respect to a predicted cavity position of the inspection object. Radiating means, detecting means for detecting reflected waves of the detection waves respectively emitted from the radiating means, and differences in the reflected waves corresponding to differences in frequency bands of the detected waves radiated by the radiating means. Based on the position estimation means for estimating the position of the start end and the position of the end of the cavity based on the thickness direction, and the cavity thickness for estimating the cavity thickness based on the position of the start end and the position of the end estimated by the position estimation means And estimation means.

  The cavity thickness estimation apparatus according to claim 6 is the cavity thickness estimation apparatus according to claim 5, wherein the radiating means detects a plurality of frequency bands having at least maximum frequencies different from each other at least with respect to a predicted cavity position of the inspection object. The wave is radiated while sweeping from the minimum frequency to the maximum frequency of the frequency band, and the position estimation means is configured to determine the thickness of the cavity according to the difference in separation and synthesis states of the reflected wave corresponding to the difference in the frequency band of the detection wave. The position of the start end and the end position in the vertical direction are estimated.

  The cavity thickness estimation apparatus according to claim 7 is the cavity thickness estimation apparatus according to claim 5 or 6, wherein the radiating means uses detection waves of a plurality of frequency bands whose maximum frequencies are discontinuous as detection waves, Interpolation means for interpolating reflected waves corresponding to each of the detection waves between the frequency bands is provided.

  The cavity thickness estimation apparatus according to claim 8 is the cavity thickness estimation apparatus according to any one of claims 5 to 7, wherein the radiating means radiates the detection wave in a state of being stopped at least with respect to the predicted cavity position of the inspection object. To do.

  According to the cavity thickness estimation method of claim 1, the reflected waves of the detection waves of a plurality of different frequency bands radiated at least to the predicted cavity position of the inspection object are respectively detected, and the difference in the frequency bands of the detection waves is determined. By estimating the start position and the end position of the cavity thickness direction based on the difference in the corresponding reflected wave, and estimating the cavity thickness based on the estimated start position and end position, The thickness of the cavity existing locally in the inspection object can be easily evaluated without destroying the inspection object.

  According to the cavity thickness estimation method according to claim 2, in addition to the effect of the cavity thickness estimation method according to claim 1, there is a case where the cavity thickness is relatively large and small with respect to the wavelength of the detection wave. Since the state of separation and synthesis of reflected waves is different between the start position and the end position of the cavity, detection of a plurality of frequency bands having at least different maximum frequencies at least with respect to the predicted cavity position of the inspection object Waves are radiated while sweeping from the minimum frequency to the maximum frequency of the frequency band, and the reflected waves of these detected waves are detected, respectively, and the difference in the state of separation and synthesis of the reflected waves corresponding to the difference in the frequency band of the detected waves Thus, by estimating the position of the start end and the end position in the thickness direction of the cavity, the start end and end of the cavity in the thickness direction can be reliably estimated.

  According to the cavity thickness estimation method according to claim 3, in addition to the effect of the cavity thickness estimation method according to claim 1 or 2, detection waves in a plurality of frequency bands whose maximum frequencies are discontinuous with each other are used. By interpolating the reflected wave corresponding to each of the frequency bands between the frequency bands, the maximum frequency of each frequency band of the detected wave does not need to be changed more finely than necessary, so that the cavity thickness can be estimated in a shorter time.

  According to the cavity thickness estimation method according to claim 4, in addition to the effect of the cavity thickness estimation method according to any one of claims 1 to 3, the detection wave is at least stopped with respect to the expected cavity position of the inspection object. , The thickness of the cavity can be more easily evaluated without using a vehicle such as an exploration vehicle.

  According to the cavity thickness estimation apparatus of claim 5, the detection means detects the reflected waves of the detection waves of a plurality of different frequency bands radiated from the radiation means at least with respect to the predicted cavity position of the inspection object, and the detection waves Based on the difference in the reflected wave corresponding to the difference in frequency band, the position of the start end and the end position in the thickness direction of the cavity are estimated by the position estimation means, and the estimated start position and end position are determined. Based on the estimation of the cavity thickness based on the cavity thickness estimation means, it is possible to easily evaluate the thickness of the cavity existing locally in the inspection object without destroying the inspection object.

  According to the cavity thickness estimation apparatus according to claim 6, in addition to the effect of the cavity thickness estimation apparatus according to claim 5, depending on whether the cavity thickness is relatively large or small with respect to the wavelength of the detection wave Since the state of separation and synthesis of the reflected waves is different between the start position and the end position of the cavity, the radiation means has a plurality of at least maximum frequencies different from each other at least with respect to the expected cavity position of the inspection object. The detection wave in the frequency band is radiated while sweeping from the minimum frequency to the maximum frequency in the frequency band, and the cavity is generated by the difference in separation and synthesis state of the reflected wave detected by the detection means corresponding to the difference in the frequency band of the detection wave. By estimating the position of the start end and the end position in the thickness direction by the position estimation means, the start end and end in the thickness direction of the cavity can be reliably estimated.

  According to the cavity thickness estimation apparatus according to claim 7, in addition to the effect of the cavity thickness estimation apparatus according to claim 5 or 6, the radiating means uses detection waves in a plurality of frequency bands whose maximum frequencies are discontinuous with each other. By interpolating the reflected wave corresponding to each of these detected waves between the frequency bands by the interpolation means, it is not necessary to set the maximum frequency of each frequency band of the detected wave more finely than necessary. It can be estimated in a shorter time.

  According to the cavity thickness estimation apparatus according to claim 8, in addition to the effect of the cavity thickness estimation apparatus according to any one of claims 5 to 7, the radiation means is stopped at least with respect to the expected cavity position of the inspection object. By emitting detection waves in a state, the thickness of the cavity can be more easily evaluated without using a vehicle such as an exploration vehicle.

It is explanatory drawing which shows the cavity thickness estimation method by the cavity thickness estimation apparatus of one embodiment of this invention. It is a flowchart which shows a process of a cavity thickness estimation method same as the above. It is the chart which put in order the reflective wave of a several different frequency band used for a cavity thickness estimation method same as the above. It is explanatory drawing which shows the production | generation method of the chart used for a cavity thickness estimation method same as the above. It is explanatory drawing which shows typically the state of isolation | separation and the synthesis | combination of a reflected wave with respect to the difference in cavity thickness in a cavity thickness estimation method same as the above. It is explanatory drawing which shows typically the state of isolation | separation and the synthesis | combination of the reflected wave corresponding to the difference in the frequency (wavelength) of the electromagnetic waves in a cavity thickness estimation method same as the above. It is explanatory drawing which shows the test target object used for the 1st experiment by a cavity thickness estimation method same as the above. It is a table | surface which shows the example of the frequency band of the detection wave radiated | emitted with respect to the test object of 1st experiment same as the above. It is explanatory drawing which shows the chart produced | generated by the 1st experiment same as the above (a) thru | or (c). It is explanatory drawing which shows the chart produced | generated by the 2nd experiment by the cavity thickness estimation method same as the above (a) and (b). The comparison between the cavity thickness estimated by the second experiment and the boring result is shown, (a) is the graph, and (b) is the table.

  The configuration of an embodiment of the present invention will be described below with reference to the drawings.

  In FIG. 1, reference numeral 11 denotes a cavity thickness estimation device. This cavity thickness estimation device 11 is used for estimating the thickness of the cavity 13 generated at the lower part of the road 12 as an inspection object, that is, the cavity thickness T. is there. In this embodiment, for example, when the road 12 is asphalt pavement, the cavity 13 is generated during pavement or between the pavement and the roadbed, but at any other position below the road surface. The generated cavity may be used, or a cavity formed between an object to be inspected other than the road 12, such as a tunnel, retaining wall or revetment, and its installation part, or a cavity generated in an object to be inspected such as a building. But you can.

  The cavity thickness estimation device 11 is a sensor having a function of a radiating means for radiating the electromagnetic wave W1 as a detection wave to the road 12 and a receiving means for receiving the reflected wave W2 of the electromagnetic wave W1 inside the road 12. An antenna 15, a network analyzer 16 having functions of signal generation means and detection means, and a computer 17 having functions of interpolation means, storage means, analysis means and display means.

  The antenna 15 is a broadband transmission antenna that functions as a transmission sensor that radiates the electromagnetic wave W1, and a broadband reception antenna that functions as a reception sensor that receives the reflected wave W2 radiated from the transmission antenna and reflected inside the road 12. It is a general thing with.

  Further, the network analyzer 16 is electrically connected to the antenna 15, generates electromagnetic waves of monocycle pulses of a plurality of different frequency bands as electromagnetic waves W1, and radiates them from the antenna 15 to the road 12. 15 is configured to detect the reflected wave W2 received. That is, the electromagnetic wave W1 incident on the road 12 undergoes a physical phenomenon of reflection / transmission in layers having different electrical properties (relative permittivity), and the reflected wave W2 is received back to the antenna 15, so the road 12 The reflected wave W2 reflected by the boundary surfaces, cavities, buried structures, etc. of each layer inside is received as a signal corresponding to the distance from the antenna 15 (road surface of the road 12).

  As the frequency band of the electromagnetic wave W1, for example, in the present embodiment, the frequency band is from a predetermined start frequency that is the minimum frequency to a predetermined stop frequency that is the maximum frequency, and this stop frequency is set for each predetermined frequency width. A plurality of different frequency bands are used. That is, the network analyzer 16 uses the antenna 15 to sweep the electromagnetic wave W1a, which is swept by frequency modulation at a predetermined number of continuous or discontinuous stages from the start frequency to the stop frequency in each of a plurality of frequency bands. It is configured to radiate to 12. Further, the network analyzer 16 generates a reflected wave W2 as a spectrum distribution obtained by detecting the reflected wave W2a of the electromagnetic wave W1a having each frequency swept in each frequency band of the generated electromagnetic wave W1.

  The computer 17 includes a calculation unit (not shown), a storage unit such as a hard disk, and a monitor. The computer 17 is electrically connected to the network analyzer 16, and receives the reflected wave W2 received by the antenna 15 and detected by the network analyzer 16. It has a function of generating a trace (reflected wave train) Tr based on the reflected wave W2 and displaying on the monitor a chart C in which these trace Trs are arranged in order of stop frequencies in the frequency band. Specifically, as shown in the order of the arrows in FIG. 4, the computer 17 performs spectrum synthesis on the reflected wave W2 corresponding to the electromagnetic wave W1 in each frequency band of the network analyzer 16 by a predetermined method such as inverse Fourier transform (IFFT). To generate trace Trs, arrange these trace Trs in the order of stop frequencies in the frequency band of electromagnetic wave W1, interpolate between those frequency bands as appropriate (collection Trs of trace Trs), and perform contrast conversion by predetermined special processing Thus, the chart C is displayed in grayscale display according to the intensity (amplitude).

  In the present embodiment, when interpolating between frequency bands of a plurality of traces Tr, for example, interpolation using an average value is used, and interpolation is performed using a plurality of, for example, 20 traces. That is, the missing data corresponding to the change in the stop frequency in the frequency band is interpolated based on the data before and after the change (data value of the trace Tr).

  For example, in the present embodiment, chart C shown in FIG. 3 is arranged such that the stop frequency increases from the right side to the left side, and the time from the start of detection increases from the upper side to the lower side. Therefore, in Chart C, the upper side is a reflected wave at a position relatively close to the surface layer of the road 12 (shallow position), and the lower side is relatively relative to the surface layer of the road 12. It is a reflected wave at a far position (deep position). In other words, in chart C, the horizontal axis represents the stop frequency and the vertical axis represents time (depth). Further, a location where the density in the chart C is relatively dark (black) corresponds to, for example, a position where the intensity (amplitude) is relatively large in the plus direction (the peak position of the trace Tr), and the density is relatively light ( The white area corresponds to the position where the intensity (amplitude) is relatively large in the negative direction (the valley position of the trace Tr). The arrangement and shading of the chart C shown in FIG. 3 are merely examples, and the arrangement and shading can be appropriately set according to predetermined rules.

  Next, the cavity thickness estimation method according to the embodiment will be described with reference to FIGS.

  First, the expected cavity position I on the road 12 is estimated by an appropriate method such as a ground penetrating radar method using an exploration vehicle (step 1). At this time, the predicted cavity position I estimates a two-dimensional spread together with the position.

  Next, the antenna 15 is placed on the road 12 at a position corresponding to the predicted cavity position I (step 2). In this arrangement, the arrangement angle with respect to the predicted cavity position I is adjusted so as to optimize the detection of the reflected wave W2 by the antenna 15 according to the shape of the expected cavity position I in the longitudinal direction and the short direction. .

  Further, the network analyzer 16 generates an electromagnetic wave W1 in a predetermined frequency band while sweeping it from a start frequency to a stop frequency in a plurality of continuous or discontinuous multiple stages (electromagnetic wave W1a). The electromagnetic wave W1 (electromagnetic wave W1a) is radiated from the antenna 15 to the road 12 (step 3). Then, the reflected wave W2 of each electromagnetic wave W1 is received by the antenna 15 and detected by the network analyzer 16 (step 4). The network analyzer 16 repeats Step 3 and Step 4 while changing the frequency band until the reflected wave W2 in all frequency bands is obtained. The reflected wave W2 in each frequency band is stored in the computer 17, respectively.

  Next, the computer 17 generates a trace Tr for each frequency band by synthesizing the spectrum of the stored reflected wave W2, generates a chart C by arranging the trace Tr in order of the stop frequency of the frequency band, and displays this chart C on the monitor. (Step 5).

  Thereafter, the operator estimates the start position and the end position in the thickness direction of the cavity 13 based on the displayed chart C (step 6). Specifically, the operator places a strip-like spot with a low density (a position where the strength (amplitude) of the trace Tr increases in the minus direction (valley position)) at a position where the stop frequency is the highest (high) in the chart C. And a portion having a deep density adjacent to the lower side of the chart C, that is, the lower side of the chart C (the position where the strength (amplitude) of the trace Tr increases in the positive direction). (Spots corresponding to (mountain position)) that are further adjacent to the darker strips, in other words, the two strips adjacent to the lighter strips are adjacent to the darker strips. When locations overlap at locations where the stop frequency is relatively small (low), the center of each of these locations (the position where the intensity (amplitude) is the highest (peak at the valley position or peak position)) The thickness direction (depth direction) of each cavity 13 Direction) and the end position. This is because the reflection / transmission of the electromagnetic wave W1 generated at the start position and the end position in the thickness direction of the cavity 13 differs depending on the frequency of the electromagnetic wave W1, and the cavity thickness with respect to the wavelength of the electromagnetic wave W1 corresponding to the stop frequency. When T is relatively large, signals indicating the position of the start end and the position of the end of the cavity 13 in the thickness direction are separated, and the cavity thickness T is relative to the wavelength of the electromagnetic wave W1 corresponding to the stop frequency. If the signal is smaller, the signals indicating the position of the start end and the position of the end of the cavity 13 in the thickness direction are synthesized (FIGS. 5 and 6). This is because it can be estimated that the position is the start position and the end position in the thickness direction of 13. For example, in the chart C shown in FIG. 3, when the strip-shaped portion B1 having a low density and the strip-shaped portion B2 adjacent to the two adjacent to the strip-shaped portion B1 are traced to the right side (side where the stop frequency is small). Since the strips B1 and B2 overlap each other on the side where the stop frequency is lower than the vicinity of the predetermined stop frequency, the central portions P1 and P2 of these strips B1 and B2 are the start ends of the cavity 13 in the thickness direction. It can be estimated that the position and the end position are indicated.

  Then, the operator detects a time difference Δt between the start position and the end position in the thickness direction of the cavity 13 based on the chart C, and estimates the cavity thickness T based on the time difference Δt (step 7). ). Specifically, when the velocity of the electromagnetic wave W1 is c, T = c · Δt / 2. Here, since the cavity 13 is filled with air, the speed c of the electromagnetic wave W1 is the same as the speed of light in the air (≈29,990,000 km / sec). The time difference Δt shown in the chart C is the time from when the electromagnetic wave W1 is radiated by the antenna 15 until the reflected wave W2 reflected at the start position or the end position of the cavity 13 is detected by the antenna 15. Therefore, since it is the time for the electromagnetic wave to reciprocate with respect to the actual start position or end position of the cavity 13, when the cavity thickness T is obtained, it is necessary to divide by 2 as in the above equation.

  In addition, after step 7, when the estimation of the cavity thickness T based on the start position and the end position in the thickness direction of the cavity 13 in the chart C is made more reliable, the cavity thickness is separately obtained using the wavelength of the electromagnetic wave W1. T is calculated.

  That is, as described above, the smaller the cavity thickness T is with respect to the wavelength of the electromagnetic wave W1, the reflected waves W2 and W2 (reflected waves W2b and W2c) that are reflected at the start and end positions in the thickness direction of the cavity 13 The time difference between them becomes smaller. Further, the wavelength of the electromagnetic wave W1 increases as the frequency decreases. Therefore, the electromagnetic wave W1 actually radiated from the antenna 15 corresponding to the frequency band having the stop frequency f1 at which interference (synthesis) between the reflected wave W2b at the start position and the reflected wave W2c at the end position starts. The length (1/2 wavelength) of the cavity thickness T is 1/2 times the length of one wavelength (because it is the time for electromagnetic waves to reciprocate with respect to the actual start position or end position of the cavity 13). Will correspond. Similarly, 1 / of the electromagnetic wave W1 actually radiated from the antenna 15 corresponding to the frequency band having the stop frequency f2 at which the reflected wave W2b at the start position and the reflected wave W2c at the end position interfere with each other at the maximum. The length (1/4 wavelength) of 1/2 of the length corresponding to 2 wavelengths (because it is the time for electromagnetic waves to reciprocate with respect to the actual position of the start or end of the cavity 13) corresponds to the cavity thickness T Will be. For this reason, one or both of the stop frequencies f1 and f2 are extracted using the chart C, and one of the wavelengths actually radiated from the antenna 15 in the frequency band having these stop frequencies f1 and f2, or By separately calculating the cavity thickness T using both, it is possible to confirm whether or not the above estimation of the cavity thickness T is appropriate.

  Specifically, when the stop frequencies f1 and f2 are extracted from the chart C, a band-like portion (band-like shape) including the position of the start end in the thickness direction (depth direction) of the cavity 13 estimated as described above. Part B1) adjacent to the high density band (band B3) and the concentration including the end position of the band (band B2) is a continuous stop frequency, that is, the band B2, The stop frequency at which the vertical gap in the chart C just disappears from B3 is the stop frequency f1, and the concentration of the strip 13 adjacent to the start position in the thickness direction (depth direction) of the cavity 13 (the strip portion) The stop frequency at which the concentration of B3) is the highest (the stop frequency at which the band B2 and the band B3 completely overlap) is defined as the stop frequency f2. The cavity thickness T is, for example, the frequency of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f1, that is, the frequency band from the predetermined start frequency to the stop frequency f1, and f1a. , C can be calculated by T = c / (2 · f1a), and is actually radiated from the antenna 15 in the frequency band where the stop frequency has the frequency f2, that is, the frequency band from the predetermined start frequency to the stop frequency f2. When the frequency of the electromagnetic wave W1 is f2a, it can be calculated by T = c / (4 · f2a). By comparing this result with the estimated cavity thickness T, the estimated cavity thickness T is reasonable. Check if it exists.

  Note that each of the above frequencies is a frequency generated by the network analyzer 16, and may not necessarily match the frequency of the electromagnetic wave W1 actually radiated from the antenna 15. Therefore, when the cavity thickness T is separately calculated as described above, it is preferable to examine the characteristics of the antenna 15 in advance and make corrections according to the characteristics of the antenna 15.

  As described above, according to the above-described embodiment, the reflected wave W2 of the electromagnetic wave W1 of a plurality of different frequency bands radiated to the predicted cavity position I of the road 12 is detected, and the frequency band difference of the electromagnetic wave W1 is detected. The start position and the end position in the thickness direction of the cavity 13 are estimated on the basis of the difference in the reflected wave W2 corresponding to, and the cavity thickness T is estimated based on the estimated start position and end position. By doing so, it is possible to easily evaluate the thickness of the cavity 13 existing locally on the back surface (lower part) of the road 12 without destroying the road 12. That is, according to the above-described embodiment, the cavity thickness T can be easily evaluated even for the locally existing cavity 13 where it is not easy to evaluate the thickness when using the ground penetrating radar device.

  Specifically, the signal reflecting the electromagnetic wave W1 at the start position and the end position in the thickness direction of the cavity 13 is separated according to the relationship between the frequency (corresponding wavelength) of the electromagnetic wave W1 and the cavity thickness T, or Synthesized. That is, when the cavity thickness T is relatively large and small with respect to the wavelength of the electromagnetic wave W1, the state of separation and synthesis of the reflected wave W2 reflected at the start position and the end position of the cavity 13 is different. . Therefore, the antenna 15 radiates and detects electromagnetic waves W1 in a plurality of frequency bands having at least different stop frequencies from the start frequency of the frequency band to the stop frequency at least with respect to the expected cavity position I of the road 12. The charts C are generated by arranging the traces Tr obtained by spectrally synthesizing the reflected waves W2 in the order of the stop frequencies. From the chart C, separation and synthesis of the reflected waves W2 corresponding to the difference in the frequency band of the electromagnetic wave W1 are generated. The position of the start end and the position of the end of the cavity 13 in the thickness direction are estimated based on the difference in state. That is, at the position where the stop frequency is the highest in Chart C, the location corresponding to the position (valley position) where the strength (amplitude) of the trace Tr increases in the minus direction and the strength of the trace Tr adjacent to this location ( The position corresponding to the position where the strength of the trace Tr adjacent to the position where the amplitude (amplitude) increases in the plus direction (mountain position) further increases in the plus direction is extracted, and these places have a relatively small stop frequency. When overlapping each other, the central part of each of these points (the position where the intensity (amplitude) is the highest (the peak at the valley position or the peak position)) is in the thickness direction (depth direction) of the cavity 13, respectively. It can be estimated that the position is the start position and the end position. As a result, the start and end of the cavity 13 in the thickness direction (depth direction) can be reliably estimated.

  And since the thickness of the cavity 13 locally existing on the road 12 can be evaluated nondestructively, it is not necessary to carry out the boring (drilling) of the road 12, and the work of backfilling is also unnecessary, and the piping Without damaging existing buried structures such as cables and cables, it is possible to reduce the work scale and to implement at low cost.

  In addition, by using electromagnetic waves W1 of multiple frequency bands where the stop frequencies are discontinuous with each other, and interpolating reflected waves W2 corresponding to each of these electromagnetic waves W1 between the frequency bands, the stop frequency of each frequency band of electromagnetic waves W1 is Since it is not necessary to change it more finely than necessary, the thickness of the cavity 13 can be estimated in a shorter time.

  Furthermore, the antenna 15 emits the electromagnetic wave W1 while stopped at least at the expected cavity position I of the road 12, so that the thickness of the cavity 13 can be more easily evaluated without using a vehicle such as an exploration vehicle, for example. it can.

  The frequency of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f1 at which the reflected wave W2b corresponding to the position of the start end of the cavity 13 and the reflected wave W2c corresponding to the position of the end start synthesis And the frequency of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f2 at which the reflected wave W2b and the reflected wave W2c interfere with each other (the wavelength corresponding to) at least. The validity of the cavity thickness T estimated by the above method can be confirmed by separately calculating the cavity thickness T using either of them.

  In the above embodiment, the estimation of the position of the start end and the position of the end of the cavity 13 in the thickness direction and the estimation of the cavity thickness T based on these positions are performed by, for example, using the computer 17 to image the chart C. You may carry out by analyzing. That is, the cavity based on the difference in the reflected wave W2 corresponding to the difference in the frequency band of the electromagnetic wave W1 radiated by the antenna 15 (the difference in the separation and synthesis state of the reflected wave W2 corresponding to the difference in the frequency band of the electromagnetic wave W1) 13 is a function of position estimation means for estimating the position of the start end and the position of the end in the thickness direction, and a cavity thickness estimation means for estimating the cavity thickness T based on the estimated start position and end position. Functions may be implemented in the computer 17.

  Further, the trace Tr of each frequency band is not limited to the one that receives the reflected wave of the electromagnetic wave W1 radiated by the antenna 15 in a stopped state. The reflected wave measured by the device) is subjected to spectrum analysis by Fast Fourier Transform (FFT), the data of the target frequency band is extracted from the spectrum, and each spectrum is synthesized by inverse Fourier transform (IFFT), etc. Also good.

  Further, the chart C may be displayed in a color display having a different color arrangement corresponding to the intensity (amplitude) of the trace Tr, for example, instead of the grayscale shading display.

  The network analyzer 16 may have functions such as interpolation means, storage means, or display means.

  Next, a first experiment by the cavity thickness estimation method of the above embodiment will be described.

  In this first experiment, an inspection object 21 shown in FIG. 7 was used. This inspection object 21 is a main body portion in which a plate material 23 such as a concrete panel is arranged at a position excluding the upper side of the frame body 22 with respect to a frame body 22 formed in a rectangular parallelepiped frame shape using, for example, an L-shaped angle. 24, a vinyl sheet or the like (not shown) was pasted inside the main body 24, and sand was put into the main body 24 from above. Then, the antenna 15 is attached to the plate member 23a that forms one surface of the main body 24, and the reflection plate is disposed on the opposite side of the plate member 23a of the plate member 23b that faces the plate member 23a, that is, on the back side of the antenna 15. 25 is attached to the frame body 22, and the reflection plate 25 is movable along the frame body 22, thereby making the distance L between the plate material 23b and the reflection plate 25 variable, and by changing the distance L, the plate material 23b and The thickness of the cavity 13 formed between the reflector 25 and the reflector 25 is configured to change.

  In the first experiment, as the frequency band of the electromagnetic wave W1 generated by the network analyzer 16, a start frequency is fixed at 300 kHz, and a stop frequency is set from 3000 MHz to 500 MHz every 100 MHz. Was used (FIG. 8).

  And the chart produced | generated with respect to the test object 21 in three positions which increased the thickness L of the cavity 13 from 200 mm to 400 mm by 100 mm gradually by increasing the distance L of the board | plate material 23b and the reflecting plate 25 gradually. C1 to C3 are shown in FIGS. 9 (a) to 9 (c).

  First, in the chart C1, at the position where the stop frequency is the highest (near the left end), the location corresponding to the position where the strength (amplitude) of the trace Tr increases in the negative direction (valley position) ) And the location corresponding to the position (mountain position) where the strength (amplitude) of the adjacent trace Tr increases in the positive direction next to this location (the band-like portion B5 where the concentration is high) Since the strips B4 and B5 are overlapped on the side where the stop frequency is smaller than the vicinity of the predetermined stop frequency (right side), the central portions P4 and P5 of these strips B4 and B5 are the thickness of the cavity 13, respectively. It can be estimated that the position is the start position and the end position of the direction.

  By the same operation, in each of the charts C2 and C3, the central portions P6 and P7 of the belt-like portions B6 and B7 and the central portions P8 and P9 of the belt-like portions B8 and B9 are positioned at the start ends in the thickness direction of the cavity 13. And the position of the end.

  And between the central portions P4 and P5 of the strip portions B4 and B5 of these charts C1 to C3, between the central portions P6 and P7 of the strip portions B6 and B7, and between the central portions P8 and P9 of the strip portions B8 and B9, respectively. Is about 1.3 ns, about 2.0 ns, and about 2.6 ns, and the obtained cavity thickness T can be estimated to be about 194 mm, about 299 mm, and about 388 mm, respectively. That is, it was shown that the cavity thickness T estimated in each of the charts C1 to C3 accurately corresponds to the actual thickness of the cavity 13.

  Next, a second experiment by the cavity thickness estimation method of the above embodiment will be described.

  In this second experiment, the cavity thickness estimation method of the above-described embodiment was applied to an actual asphalt pavement road 12.

  In this second experiment, a chart C4 (FIG. 10 (a)) is generated based on the reflected wave W2 measured by placing the antenna 15 at the expected cavity position I, and the antenna 15 is positioned near the expected cavity position I. The chart C5 (FIG. 10 (b)) is generated based on the reflected wave W2 measured at the position outside the predicted cavity position I. The frequency band of the electromagnetic wave W1 generated by the network analyzer 16 was the same as in the first experiment.

  Then, by comparing the chart C4 and the chart C5, the signal (shading band) located in the area A1 in the chart C4 is also present in the area A2 in the chart C5 corresponding to the area A1. From these, it is assumed that these signals are generated independently of the cavity 13. In other words, in the case of the asphalt pavement road 12, the electromagnetic wave W1 is reflected even at the boundary surface between the surface layer and the base layer of the pavement. Therefore, the signals present in the above regions A1 and A2 are the signals generated at such a boundary surface. It is estimated that. Therefore, in Chart C4, the position of the start end and the end position in the thickness direction of the cavity 13 were estimated at positions excluding the region A1.

  Specifically, at the position excluding the area A1 of the chart C4, at the position where the stop frequency is the highest (near the left end), the location corresponding to the position where the strength (amplitude) of the trace Tr increases in the negative direction (valley position) ( A lightly strip-shaped part B10) and a part corresponding to a position (mountain position) where the strength (amplitude) of the adjacent trace Tr adjacent to this part becomes larger in the positive direction (highly-concentrated belt-like part B11) When each is extracted, these band-like parts B10, B11 are overlapped on the side where the stop frequency is smaller than the vicinity of the predetermined stop frequency (right side), so the central parts P10, P11 of these band-like parts B10, B11 are It can be estimated that the position is the start position and the end position of the cavity 13 in the thickness direction.

  Then, the cavity thickness T estimated with respect to the predicted cavity position I (inspection positions (1) to (4)) of a plurality of roads 12, and the result of measuring the cavity thickness by boring each of these predicted cavity positions I Is shown in FIGS. 11 (a) and 11 (b).

  Thus, the cavity thickness T estimated based on the cavity thickness estimation method of the above-described embodiment and the cavity thickness actually measured by boring have an error of about 10% or less. It has been shown that the estimation of the cavity thickness T by the cavity thickness estimation method of the above-described embodiment is also effective for the actual road 12 having the cavity 13 having the generation depth.

  Further, the chart C4 generated based on the reflected wave W2 detected at the predicted cavity position I by using the chart C5 generated based on the reflected wave W2 detected at the position outside the predicted cavity position I as a comparison object. Therefore, it is possible to exclude a signal that is assumed to be generated independently of the cavity 13, and thus it is possible to accurately estimate the position of the start end and the end position of the cavity 13 in the thickness direction in a shorter time.

  In the first and second experiments, the reflected wave W2b corresponding to the start position of the cavity 13 and the reflected wave W2c corresponding to the end position are combined in order to more reliably estimate the cavity thickness T. The wavelength of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f1 to start the operation and the actual frequency from the antenna 15 in the frequency band having the stop frequency f2 where the reflected wave W2b and the reflected wave W2c interfere with each other The cavity thickness T may be calculated separately by using at least one of the wavelength of the electromagnetic wave W1 radiated to.

11 Cavity thickness estimation device
12 Road as inspection object
13 cavity
15 Antenna having the function of radiation means
16 Network analyzer with detection function
17 Computer with interpolating function I Expected cavity position
W1 Electromagnetic waves that are detected waves
W2 reflected wave

  The present invention relates to a cavity thickness estimation method and apparatus for estimating a cavity thickness of an inspection object.

  In general, for evaluating the thickness of a cavity in an inspection object such as a road, tunnel, retaining wall, revetment, or building, an electromagnetic ground penetrating radar device is moved by an exploration vehicle or human power. Thus, the reflected wave of the electromagnetic wave radiated toward the inspection object is detected, and the detection wave is analyzed to perform nondestructive.

  However, such an evaluation is possible when the cavities are continuous with a certain length, for example, the cavities present at the back of the tunnel, but locally, such as cavities under paved roads. For existing cavities, it is only possible to measure the planar spread, and it is not easy to evaluate the thickness because the amount of information with respect to the movement distance of the underground radar apparatus is small. Therefore, generally, a method is used in which the state inside the cavity is visually confirmed by boring the target object at the predicted cavity position detected by the ground penetrating radar device (see, for example, Patent Document 1). .

Japanese Patent Laid-Open No. 5-87945 (page 3-5, FIG. 1-8)

  However, in the case of the method as described above, it is necessary to drill a hole in the inspection object as a result, so that a part of the inspection object is destroyed and work such as backfilling is required. At the same time, there is a concern that existing buried structures such as pipes and cables may be damaged, and there is a problem that the work becomes large and complicated.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a cavity thickness estimation method and apparatus capable of easily evaluating the thickness of a cavity locally present in an inspection object in a nondestructive manner. To do.

The cavity thickness estimation method according to claim 1 is a cavity thickness estimation method for estimating a cavity thickness of an inspection object , and at least a plurality of frequencies having different maximum frequencies from each other, at least with respect to an estimated cavity position of the inspection object. The detection wave of the band is radiated while sweeping from the minimum frequency to the maximum frequency of the frequency band, the reflected wave of these detection waves is detected, and the trace for each frequency band of the detected reflected wave is traced in this frequency band. A chart is generated by arranging in order of maximum frequency. From this chart, the peak position where the intensity of the trace increases in the negative direction at the position where the maximum frequency is the maximum, and the two adjacent on the side that is later in time than this peak position. The peak positions where the intensity of the trace adjacent to each other increases in the positive direction are extracted, and these peak positions are the maximum circumference in the chart. If the number is overlapped at a relatively low point, these located and estimated in the thickness direction of the start position and end of the cavity a peak position, based on the positions of these start positions and end estimated Thus, the cavity thickness is estimated.

Cavity thickness estimation method 請 Motomeko 2 wherein, in the cavity thickness estimation method according to claim 1, wherein, as the detection wave, using detection wave of maximum frequency from each other a plurality of discontinuous frequency bands, each of the detection wave The corresponding reflected wave is interpolated between frequency bands.

According to a third aspect of the present invention, in the method for estimating the cavity thickness according to the first or second aspect , the detection wave is radiated at least with respect to a predicted cavity position of the inspection object.

5. The cavity thickness estimation apparatus according to claim 4, wherein the cavity thickness estimation apparatus estimates a cavity thickness of an object to be inspected, and at least a plurality of frequencies whose maximum frequencies are different from each other at least with respect to an estimated cavity position of the object to be inspected. A radiation means for radiating a detection wave in a band while sweeping from a minimum frequency to a maximum frequency in the frequency band, a detection means for detecting a reflected wave of the detection wave radiated from the radiation means, and a detection means From the chart generated by arranging the traces of each reflected wave for each frequency band in order of the maximum frequency of this frequency band, the peak position where the intensity of the trace increases in the negative direction at the position where the maximum frequency is the highest, and this peak The peak positions where the intensity of the adjacent traces adjacent to the two sides on the side later in time than the position increase in the positive direction are extracted. And, these peak positions, if the maximum frequency in the chart are overlapping at a relatively low position, to position and estimated in the thickness direction of the start position and end of the cavity of these peak positions Position An estimation means and a cavity thickness estimation means for estimating the cavity thickness based on the position of the start end and the position of the end estimated by the position estimation means are provided.

Cavity thickness estimation device 請 Motomeko 5 wherein, in the cavity thickness estimation device according to claim 4, wherein the radiation means, as the detection wave, using detection wave of maximum frequency from each other a plurality of discontinuous frequency bands, the detection Interpolation means for interpolating the reflected wave corresponding to each of the waves between the frequency bands is provided.

The cavity thickness estimation apparatus according to claim 6 is the cavity thickness estimation apparatus according to claim 4 or 5, wherein the radiating means radiates the detection wave in a state where it is stopped at least with respect to the predicted cavity position of the inspection object. is there.

According to the cavity thickness estimation method according to claim 1 , the reflection reflected at the start position and the end position of the cavity when the thickness of the cavity is relatively large or small with respect to the wavelength of the detection wave. Since the state of wave separation and synthesis is different, at least for the expected cavity position of the object to be inspected , the detection waves of a plurality of frequency bands having different maximum frequencies are swept from the minimum frequency to the maximum frequency of the frequency band. The reflected waves are detected respectively, and the traces for each frequency band of the detected reflected waves are arranged in the order of the maximum frequency of the frequency band. The peak position where the intensity increases in the minus direction, and the intensity of the trace adjacent to the two adjacent to the side later in time than this peak position is increased in the plus direction. That the peak position respectively extracted, these peak positions, if the maximum frequency in the chart are overlapped at a relatively low position, the cavities of these peak positions in the thickness direction starting end position and the end of the position and then estimated, by estimating the cavity thickness based on the positions of the end of these start estimated thickness of the cavity that exists locally on the test object without destroying the test object Can be easily and reliably evaluated.

According to the cavity thickness estimation method 請 Motomeko 2 wherein, in addition to the effect of cavity thickness estimation method according to claim 1, wherein, using a detection wave of maximum frequency is a plurality of discontinuous frequency bands, these detection wave By interpolating the corresponding reflected waves between the frequency bands, the maximum frequency of each frequency band of the detection wave does not need to be changed more finely than necessary, so that the cavity thickness can be estimated in a shorter time.

According to the cavity thickness estimation method according to claim 3, wherein, in addition to the effect of cavity thickness estimation method according to claim 1, which emit detectable wave in a stopped state relative to the cavity expected position of at least test object Thus, for example, the thickness of the cavity can be more easily evaluated without using a vehicle such as an exploration vehicle.

According to the cavity thickness estimation apparatus according to claim 4 , the reflection reflected at the position of the start end and the position of the end of the cavity when the thickness of the cavity is relatively large or small with respect to the wavelength of the detection wave. Since the state of separation and synthesis of the waves is different, the radiating means at least detects the detected waves in a plurality of frequency bands having different maximum frequencies from the minimum frequency in the frequency band at least with respect to the expected cavity position of the inspection object. Radiated while sweeping to the frequency, the reflected waves of the detected waves of a plurality of different frequency bands radiated are respectively detected by the detecting means , and the trace for each frequency band of each reflected wave detected by the detecting means is traced in this frequency band. The peak position where the intensity of the trace increases in the negative direction at the position where the maximum frequency is the highest in the chart generated in order of the maximum frequency, and this peak. The peak positions where the intensity of the traces adjacent to the two adjacent to the side that is later in time than the position increases in the positive direction are extracted, respectively, and these peak positions are at locations where the maximum frequency in the chart is relatively low. If the overlap, is estimated by the position estimating means and the position in the thickness direction of the start position and end of the cavity of these peak positions, the cavity on the basis of the positions of the end of these start estimated By estimating the thickness by the cavity thickness estimating means, the thickness of the cavity locally existing in the inspection object can be easily and reliably evaluated without destroying the inspection object.

According to the cavity thickness estimation device 請 Motomeko 5 wherein, in addition to the effect of cavity thickness estimation device according to claim 4, wherein the radiation means, using the detection wave of the maximum frequency with one another a plurality of discontinuous frequency bands, By interpolating the reflected wave corresponding to each of these detected waves between the frequency bands by interpolation means, it is not necessary to set the maximum frequency of each frequency band of the detected wave more finely than necessary, so the thickness of the cavity can be further increased. It can be estimated in a short time.

According to the cavity thickness estimation apparatus according to claim 6 , in addition to the effect of the cavity thickness estimation apparatus according to claim 4 or 5 , detection is performed in a state in which the radiation means is stopped at least with respect to the expected cavity position of the inspection object. By emitting waves, the thickness of the cavity can be more easily evaluated without using a vehicle such as an exploration vehicle.

It is explanatory drawing which shows the cavity thickness estimation method by the cavity thickness estimation apparatus of one embodiment of this invention. It is a flowchart which shows a process of a cavity thickness estimation method same as the above. It is the chart which put in order the reflective wave of a several different frequency band used for a cavity thickness estimation method same as the above. It is explanatory drawing which shows the production | generation method of the chart used for a cavity thickness estimation method same as the above. It is explanatory drawing which shows typically the state of isolation | separation and the synthesis | combination of a reflected wave with respect to the difference in cavity thickness in a cavity thickness estimation method same as the above. It is explanatory drawing which shows typically the state of isolation | separation and the synthesis | combination of the reflected wave corresponding to the difference in the frequency (wavelength) of the electromagnetic waves in a cavity thickness estimation method same as the above. It is explanatory drawing which shows the test target object used for the 1st experiment by a cavity thickness estimation method same as the above. It is a table | surface which shows the example of the frequency band of the detection wave radiated | emitted with respect to the test object of 1st experiment same as the above. It is explanatory drawing which shows the chart produced | generated by the 1st experiment same as the above (a) thru | or (c). It is explanatory drawing which shows the chart produced | generated by the 2nd experiment by the cavity thickness estimation method same as the above (a) and (b). The comparison between the cavity thickness estimated by the second experiment and the boring result is shown, (a) is the graph, and (b) is the table.

  The configuration of an embodiment of the present invention will be described below with reference to the drawings.

  In FIG. 1, reference numeral 11 denotes a cavity thickness estimation device. This cavity thickness estimation device 11 is used for estimating the thickness of the cavity 13 generated at the lower part of the road 12 as an inspection object, that is, the cavity thickness T. is there. In this embodiment, for example, when the road 12 is asphalt pavement, the cavity 13 is generated during pavement or between the pavement and the roadbed, but at any other position below the road surface. The generated cavity may be used, or a cavity formed between an object to be inspected other than the road 12, such as a tunnel, retaining wall or revetment, and its installation part, or a cavity generated in an object to be inspected such as a building. But you can.

  The cavity thickness estimation device 11 is a sensor having a function of a radiating means for radiating the electromagnetic wave W1 as a detection wave to the road 12 and a receiving means for receiving the reflected wave W2 of the electromagnetic wave W1 inside the road 12. An antenna 15, a network analyzer 16 having functions of signal generation means and detection means, and a computer 17 having functions of interpolation means, storage means, analysis means and display means.

  The antenna 15 is a broadband transmission antenna that functions as a transmission sensor that radiates the electromagnetic wave W1, and a broadband reception antenna that functions as a reception sensor that receives the reflected wave W2 radiated from the transmission antenna and reflected inside the road 12. It is a general thing with.

  Further, the network analyzer 16 is electrically connected to the antenna 15, generates electromagnetic waves of monocycle pulses of a plurality of different frequency bands as electromagnetic waves W1, and radiates them from the antenna 15 to the road 12. 15 is configured to detect the reflected wave W2 received. That is, the electromagnetic wave W1 incident on the road 12 undergoes a physical phenomenon of reflection / transmission in layers having different electrical properties (relative permittivity), and the reflected wave W2 is received back to the antenna 15, so the road 12 The reflected wave W2 reflected by the boundary surfaces, cavities, buried structures, etc. of each layer inside is received as a signal corresponding to the distance from the antenna 15 (road surface of the road 12).

  As the frequency band of the electromagnetic wave W1, for example, in the present embodiment, the frequency band is from a predetermined start frequency that is the minimum frequency to a predetermined stop frequency that is the maximum frequency, and this stop frequency is set for each predetermined frequency width. A plurality of different frequency bands are used. That is, the network analyzer 16 uses the antenna 15 to sweep the electromagnetic wave W1a, which is swept by frequency modulation at a predetermined number of continuous or discontinuous stages from the start frequency to the stop frequency in each of a plurality of frequency bands. It is configured to radiate to 12. Further, the network analyzer 16 generates a reflected wave W2 as a spectrum distribution obtained by detecting the reflected wave W2a of the electromagnetic wave W1a having each frequency swept in each frequency band of the generated electromagnetic wave W1.

  The computer 17 includes a calculation unit (not shown), a storage unit such as a hard disk, and a monitor. The computer 17 is electrically connected to the network analyzer 16, and receives the reflected wave W2 received by the antenna 15 and detected by the network analyzer 16. It has a function of generating a trace (reflected wave train) Tr based on the reflected wave W2 and displaying on the monitor a chart C in which these trace Trs are arranged in order of stop frequencies in the frequency band. Specifically, as shown in the order of the arrows in FIG. 4, the computer 17 performs spectrum synthesis on the reflected wave W2 corresponding to the electromagnetic wave W1 in each frequency band of the network analyzer 16 by a predetermined method such as inverse Fourier transform (IFFT). To generate trace Trs, arrange these trace Trs in the order of stop frequencies in the frequency band of electromagnetic wave W1, interpolate between those frequency bands as appropriate (collection Trs of trace Trs), and perform contrast conversion by predetermined special processing Thus, the chart C is displayed in grayscale display according to the intensity (amplitude).

  In the present embodiment, when interpolating between frequency bands of a plurality of traces Tr, for example, interpolation using an average value is used, and interpolation is performed using a plurality of, for example, 20 traces. That is, the missing data corresponding to the change in the stop frequency in the frequency band is interpolated based on the data before and after the change (data value of the trace Tr).

  For example, in the present embodiment, chart C shown in FIG. 3 is arranged such that the stop frequency increases from the right side to the left side, and the time from the start of detection increases from the upper side to the lower side. Therefore, in Chart C, the upper side is a reflected wave at a position relatively close to the surface layer of the road 12 (shallow position), and the lower side is relatively relative to the surface layer of the road 12. It is a reflected wave at a far position (deep position). In other words, in chart C, the horizontal axis represents the stop frequency and the vertical axis represents time (depth). Further, a location where the density in the chart C is relatively dark (black) corresponds to, for example, a position where the intensity (amplitude) is relatively large in the plus direction (the peak position of the trace Tr), and the density is relatively light ( The white area corresponds to the position where the intensity (amplitude) is relatively large in the negative direction (the valley position of the trace Tr). The arrangement and shading of the chart C shown in FIG. 3 are merely examples, and the arrangement and shading can be appropriately set according to predetermined rules.

  Next, the cavity thickness estimation method according to the embodiment will be described with reference to FIGS.

  First, the expected cavity position I on the road 12 is estimated by an appropriate method such as a ground penetrating radar method using an exploration vehicle (step 1). At this time, the predicted cavity position I estimates a two-dimensional spread together with the position.

  Next, the antenna 15 is placed on the road 12 at a position corresponding to the predicted cavity position I (step 2). In this arrangement, the arrangement angle with respect to the predicted cavity position I is adjusted so as to optimize the detection of the reflected wave W2 by the antenna 15 according to the shape of the expected cavity position I in the longitudinal direction and the short direction. .

  Further, the network analyzer 16 generates an electromagnetic wave W1 in a predetermined frequency band while sweeping it from a start frequency to a stop frequency in a plurality of continuous or discontinuous multiple stages (electromagnetic wave W1a). The electromagnetic wave W1 (electromagnetic wave W1a) is radiated from the antenna 15 to the road 12 (step 3). Then, the reflected wave W2 of each electromagnetic wave W1 is received by the antenna 15 and detected by the network analyzer 16 (step 4). The network analyzer 16 repeats Step 3 and Step 4 while changing the frequency band until the reflected wave W2 in all frequency bands is obtained. The reflected wave W2 in each frequency band is stored in the computer 17, respectively.

  Next, the computer 17 generates a trace Tr for each frequency band by synthesizing the spectrum of the stored reflected wave W2, generates a chart C by arranging the trace Tr in order of the stop frequency of the frequency band, and displays this chart C on the monitor. (Step 5).

  Thereafter, the operator estimates the start position and the end position in the thickness direction of the cavity 13 based on the displayed chart C (step 6). Specifically, the operator places a strip-like spot with a low density (a position where the strength (amplitude) of the trace Tr increases in the minus direction (valley position)) at a position where the stop frequency is the highest (high) in the chart C. And a portion having a deep density adjacent to the lower side of the chart C, that is, the lower side of the chart C (the position where the strength (amplitude) of the trace Tr increases in the positive direction). (Spots corresponding to (mountain position)) that are further adjacent to the darker strips, in other words, the two strips adjacent to the lighter strips are adjacent to the darker strips. When locations overlap at locations where the stop frequency is relatively small (low), the center of each of these locations (the position where the intensity (amplitude) is the highest (peak at the valley position or peak position)) The thickness direction (depth direction) of each cavity 13 Direction) and the end position. This is because the reflection / transmission of the electromagnetic wave W1 generated at the start position and the end position in the thickness direction of the cavity 13 differs depending on the frequency of the electromagnetic wave W1, and the cavity thickness with respect to the wavelength of the electromagnetic wave W1 corresponding to the stop frequency. When T is relatively large, signals indicating the position of the start end and the position of the end of the cavity 13 in the thickness direction are separated, and the cavity thickness T is relative to the wavelength of the electromagnetic wave W1 corresponding to the stop frequency. If the signal is smaller, the signals indicating the position of the start end and the position of the end of the cavity 13 in the thickness direction are synthesized (FIGS. 5 and 6). This is because it can be estimated that the position is the start position and the end position in the thickness direction of 13. For example, in the chart C shown in FIG. 3, when the strip-shaped portion B1 having a low density and the strip-shaped portion B2 adjacent to the two adjacent to the strip-shaped portion B1 are traced to the right side (side where the stop frequency is small). Since the strips B1 and B2 overlap each other on the side where the stop frequency is lower than the vicinity of the predetermined stop frequency, the central portions P1 and P2 of these strips B1 and B2 are the start ends of the cavity 13 in the thickness direction. It can be estimated that the position and the end position are indicated.

  Then, the operator detects a time difference Δt between the start position and the end position in the thickness direction of the cavity 13 based on the chart C, and estimates the cavity thickness T based on the time difference Δt (step 7). ). Specifically, when the velocity of the electromagnetic wave W1 is c, T = c · Δt / 2. Here, since the cavity 13 is filled with air, the speed c of the electromagnetic wave W1 is the same as the speed of light in the air (≈29,990,000 km / sec). The time difference Δt shown in the chart C is the time from when the electromagnetic wave W1 is radiated by the antenna 15 until the reflected wave W2 reflected at the start position or the end position of the cavity 13 is detected by the antenna 15. Therefore, since it is the time for the electromagnetic wave to reciprocate with respect to the actual start position or end position of the cavity 13, when the cavity thickness T is obtained, it is necessary to divide by 2 as in the above equation.

  In addition, after step 7, when the estimation of the cavity thickness T based on the start position and the end position in the thickness direction of the cavity 13 in the chart C is made more reliable, the cavity thickness is separately obtained using the wavelength of the electromagnetic wave W1. T is calculated.

  That is, as described above, the smaller the cavity thickness T is with respect to the wavelength of the electromagnetic wave W1, the reflected waves W2 and W2 (reflected waves W2b and W2c) that are reflected at the start and end positions in the thickness direction of the cavity 13 The time difference between them becomes smaller. Further, the wavelength of the electromagnetic wave W1 increases as the frequency decreases. Therefore, the electromagnetic wave W1 actually radiated from the antenna 15 corresponding to the frequency band having the stop frequency f1 at which interference (synthesis) between the reflected wave W2b at the start position and the reflected wave W2c at the end position starts. The length (1/2 wavelength) of the cavity thickness T is 1/2 times the length of one wavelength (because it is the time for electromagnetic waves to reciprocate with respect to the actual start position or end position of the cavity 13). Will correspond. Similarly, 1 / of the electromagnetic wave W1 actually radiated from the antenna 15 corresponding to the frequency band having the stop frequency f2 at which the reflected wave W2b at the start position and the reflected wave W2c at the end position interfere with each other at the maximum. The length (1/4 wavelength) of 1/2 of the length corresponding to 2 wavelengths (because it is the time for electromagnetic waves to reciprocate with respect to the actual position of the start or end of the cavity 13) corresponds to the cavity thickness T Will be. For this reason, one or both of the stop frequencies f1 and f2 are extracted using the chart C, and one of the wavelengths actually radiated from the antenna 15 in the frequency band having these stop frequencies f1 and f2, or By separately calculating the cavity thickness T using both, it is possible to confirm whether or not the above estimation of the cavity thickness T is appropriate.

  Specifically, when the stop frequencies f1 and f2 are extracted from the chart C, a band-like portion (band-like shape) including the position of the start end in the thickness direction (depth direction) of the cavity 13 estimated as described above. Part B1) adjacent to the high density band (band B3) and the concentration including the end position of the band (band B2) is a continuous stop frequency, that is, the band B2, The stop frequency at which the vertical gap in the chart C just disappears from B3 is the stop frequency f1, and the concentration of the strip 13 adjacent to the start position in the thickness direction (depth direction) of the cavity 13 (the strip portion) The stop frequency at which the concentration of B3) is the highest (the stop frequency at which the band B2 and the band B3 completely overlap) is defined as the stop frequency f2. The cavity thickness T is, for example, the frequency of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f1, that is, the frequency band from the predetermined start frequency to the stop frequency f1, and f1a. , C can be calculated by T = c / (2 · f1a), and is actually radiated from the antenna 15 in the frequency band where the stop frequency has the frequency f2, that is, the frequency band from the predetermined start frequency to the stop frequency f2. When the frequency of the electromagnetic wave W1 is f2a, it can be calculated by T = c / (4 · f2a). By comparing this result with the estimated cavity thickness T, the estimated cavity thickness T is reasonable. Check if it exists.

  Note that each of the above frequencies is a frequency generated by the network analyzer 16, and may not necessarily match the frequency of the electromagnetic wave W1 actually radiated from the antenna 15. Therefore, when the cavity thickness T is separately calculated as described above, it is preferable to examine the characteristics of the antenna 15 in advance and make corrections according to the characteristics of the antenna 15.

  As described above, according to the above-described embodiment, the reflected wave W2 of the electromagnetic wave W1 of a plurality of different frequency bands radiated to the predicted cavity position I of the road 12 is detected, and the frequency band difference of the electromagnetic wave W1 is detected. The start position and the end position in the thickness direction of the cavity 13 are estimated on the basis of the difference in the reflected wave W2 corresponding to, and the cavity thickness T is estimated based on the estimated start position and end position. By doing so, it is possible to easily evaluate the thickness of the cavity 13 existing locally on the back surface (lower part) of the road 12 without destroying the road 12. That is, according to the above-described embodiment, the cavity thickness T can be easily evaluated even for the locally existing cavity 13 where it is not easy to evaluate the thickness when using the ground penetrating radar device.

  Specifically, the signal reflecting the electromagnetic wave W1 at the start position and the end position in the thickness direction of the cavity 13 is separated according to the relationship between the frequency (corresponding wavelength) of the electromagnetic wave W1 and the cavity thickness T, or Synthesized. That is, when the cavity thickness T is relatively large and small with respect to the wavelength of the electromagnetic wave W1, the state of separation and synthesis of the reflected wave W2 reflected at the start position and the end position of the cavity 13 is different. . Therefore, the antenna 15 radiates and detects electromagnetic waves W1 in a plurality of frequency bands having at least different stop frequencies from the start frequency of the frequency band to the stop frequency at least with respect to the expected cavity position I of the road 12. The charts C are generated by arranging the traces Tr obtained by spectrally synthesizing the reflected waves W2 in the order of the stop frequencies. From the chart C, separation and synthesis of the reflected waves W2 corresponding to the difference in the frequency band of the electromagnetic wave W1 are generated. The position of the start end and the position of the end of the cavity 13 in the thickness direction are estimated based on the difference in state. That is, at the position where the stop frequency is the highest in Chart C, the location corresponding to the position (valley position) where the strength (amplitude) of the trace Tr increases in the minus direction and the strength of the trace Tr adjacent to this location ( The position corresponding to the position where the strength of the trace Tr adjacent to the position where the amplitude (amplitude) increases in the plus direction (mountain position) further increases in the plus direction is extracted, and these places have a relatively small stop frequency. When overlapping each other, the central part of each of these points (the position where the intensity (amplitude) is the highest (the peak at the valley position or the peak position)) is in the thickness direction (depth direction) of the cavity 13, respectively. It can be estimated that the position is the start position and the end position. As a result, the start and end of the cavity 13 in the thickness direction (depth direction) can be reliably estimated.

  And since the thickness of the cavity 13 locally existing on the road 12 can be evaluated nondestructively, it is not necessary to carry out the boring (drilling) of the road 12, and the work of backfilling is also unnecessary, and the piping Without damaging existing buried structures such as cables and cables, it is possible to reduce the work scale and to implement at low cost.

  In addition, by using electromagnetic waves W1 of multiple frequency bands where the stop frequencies are discontinuous with each other, and interpolating reflected waves W2 corresponding to each of these electromagnetic waves W1 between the frequency bands, the stop frequency of each frequency band of electromagnetic waves W1 is Since it is not necessary to change it more finely than necessary, the thickness of the cavity 13 can be estimated in a shorter time.

  Furthermore, the antenna 15 emits the electromagnetic wave W1 while stopped at least at the expected cavity position I of the road 12, so that the thickness of the cavity 13 can be more easily evaluated without using a vehicle such as an exploration vehicle, for example. it can.

  The frequency of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f1 at which the reflected wave W2b corresponding to the position of the start end of the cavity 13 and the reflected wave W2c corresponding to the position of the end start synthesis And the frequency of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f2 at which the reflected wave W2b and the reflected wave W2c interfere with each other (the wavelength corresponding to) at least. The validity of the cavity thickness T estimated by the above method can be confirmed by separately calculating the cavity thickness T using either of them.

  In the above embodiment, the estimation of the position of the start end and the position of the end of the cavity 13 in the thickness direction and the estimation of the cavity thickness T based on these positions are performed by, for example, using the computer 17 to image the chart C. You may carry out by analyzing. That is, the cavity based on the difference in the reflected wave W2 corresponding to the difference in the frequency band of the electromagnetic wave W1 radiated by the antenna 15 (the difference in the separation and synthesis state of the reflected wave W2 corresponding to the difference in the frequency band of the electromagnetic wave W1) 13 is a function of position estimation means for estimating the position of the start end and the position of the end in the thickness direction, and a cavity thickness estimation means for estimating the cavity thickness T based on the estimated start position and end position. Functions may be implemented in the computer 17.

  Further, the trace Tr of each frequency band is not limited to the one that receives the reflected wave of the electromagnetic wave W1 radiated by the antenna 15 in a stopped state. The reflected wave measured by the device) is subjected to spectrum analysis by Fast Fourier Transform (FFT), the data of the target frequency band is extracted from the spectrum, and each spectrum is synthesized by inverse Fourier transform (IFFT), etc. Also good.

  Further, the chart C may be displayed in a color display having a different color arrangement corresponding to the intensity (amplitude) of the trace Tr, for example, instead of the grayscale shading display.

  The network analyzer 16 may have functions such as interpolation means, storage means, or display means.

  Next, a first experiment by the cavity thickness estimation method of the above embodiment will be described.

  In this first experiment, an inspection object 21 shown in FIG. 7 was used. This inspection object 21 is a main body portion in which a plate material 23 such as a concrete panel is arranged at a position excluding the upper side of the frame body 22 with respect to a frame body 22 formed in a rectangular parallelepiped frame shape using, for example, an L-shaped angle. 24, a vinyl sheet or the like (not shown) was pasted inside the main body 24, and sand was put into the main body 24 from above. Then, the antenna 15 is attached to the plate member 23a that forms one surface of the main body 24, and the reflection plate is disposed on the opposite side of the plate member 23a of the plate member 23b that faces the plate member 23a, that is, on the back side of the antenna 15. 25 is attached to the frame body 22, and the reflection plate 25 is movable along the frame body 22, thereby making the distance L between the plate material 23b and the reflection plate 25 variable, and by changing the distance L, the plate material 23b and The thickness of the cavity 13 formed between the reflector 25 and the reflector 25 is configured to change.

  In the first experiment, as the frequency band of the electromagnetic wave W1 generated by the network analyzer 16, a start frequency is fixed at 300 kHz, and a stop frequency is set from 3000 MHz to 500 MHz every 100 MHz. Was used (FIG. 8).

  And the chart produced | generated with respect to the test object 21 in three positions which increased the thickness L of the cavity 13 from 200 mm to 400 mm by 100 mm gradually by increasing the distance L of the board | plate material 23b and the reflecting plate 25 gradually. C1 to C3 are shown in FIGS. 9 (a) to 9 (c).

  First, in the chart C1, at the position where the stop frequency is the highest (near the left end), the location corresponding to the position where the strength (amplitude) of the trace Tr increases in the negative direction (valley position) ) And the location corresponding to the position (mountain position) where the strength (amplitude) of the adjacent trace Tr increases in the positive direction next to this location (the band-like portion B5 where the concentration is high) Since the strips B4 and B5 are overlapped on the side where the stop frequency is smaller than the vicinity of the predetermined stop frequency (right side), the central portions P4 and P5 of these strips B4 and B5 are the thickness of the cavity 13, respectively. It can be estimated that the position is the start position and the end position of the direction.

  By the same operation, in each of the charts C2 and C3, the central portions P6 and P7 of the belt-like portions B6 and B7 and the central portions P8 and P9 of the belt-like portions B8 and B9 are positioned at the start ends in the thickness direction of the cavity 13. And the position of the end.

  And between the central portions P4 and P5 of the strip portions B4 and B5 of these charts C1 to C3, between the central portions P6 and P7 of the strip portions B6 and B7, and between the central portions P8 and P9 of the strip portions B8 and B9, respectively. Is about 1.3 ns, about 2.0 ns, and about 2.6 ns, and the obtained cavity thickness T can be estimated to be about 194 mm, about 299 mm, and about 388 mm, respectively. That is, it was shown that the cavity thickness T estimated in each of the charts C1 to C3 accurately corresponds to the actual thickness of the cavity 13.

  Next, a second experiment by the cavity thickness estimation method of the above embodiment will be described.

  In this second experiment, the cavity thickness estimation method of the above-described embodiment was applied to an actual asphalt pavement road 12.

  In this second experiment, a chart C4 (FIG. 10 (a)) is generated based on the reflected wave W2 measured by placing the antenna 15 at the expected cavity position I, and the antenna 15 is positioned near the expected cavity position I. The chart C5 (FIG. 10 (b)) is generated based on the reflected wave W2 measured at the position outside the predicted cavity position I. The frequency band of the electromagnetic wave W1 generated by the network analyzer 16 was the same as in the first experiment.

  Then, by comparing the chart C4 and the chart C5, the signal (shading band) located in the area A1 in the chart C4 is also present in the area A2 in the chart C5 corresponding to the area A1. From these, it is assumed that these signals are generated independently of the cavity 13. In other words, in the case of the asphalt pavement road 12, the electromagnetic wave W1 is reflected even at the boundary surface between the surface layer and the base layer of the pavement. Therefore, the signals present in the above regions A1 and A2 are the signals generated at such a boundary surface. It is estimated that. Therefore, in Chart C4, the position of the start end and the end position in the thickness direction of the cavity 13 were estimated at positions excluding the region A1.

  Specifically, at the position excluding the area A1 of the chart C4, at the position where the stop frequency is the highest (near the left end), the location corresponding to the position where the strength (amplitude) of the trace Tr increases in the negative direction (valley position) ( A lightly strip-shaped part B10) and a part corresponding to a position (mountain position) where the strength (amplitude) of the adjacent trace Tr adjacent to this part becomes larger in the positive direction (highly-concentrated belt-like part B11) When each is extracted, these band-like parts B10, B11 are overlapped on the side where the stop frequency is smaller than the vicinity of the predetermined stop frequency (right side), so the central parts P10, P11 of these band-like parts B10, B11 are It can be estimated that the position is the start position and the end position of the cavity 13 in the thickness direction.

  Then, the cavity thickness T estimated with respect to the predicted cavity position I (inspection positions (1) to (4)) of a plurality of roads 12, and the result of measuring the cavity thickness by boring each of these predicted cavity positions I Is shown in FIGS. 11 (a) and 11 (b).

  Thus, the cavity thickness T estimated based on the cavity thickness estimation method of the above-described embodiment and the cavity thickness actually measured by boring have an error of about 10% or less. It has been shown that the estimation of the cavity thickness T by the cavity thickness estimation method of the above-described embodiment is also effective for the actual road 12 having the cavity 13 having the generation depth.

  Further, the chart C4 generated based on the reflected wave W2 detected at the predicted cavity position I by using the chart C5 generated based on the reflected wave W2 detected at the position outside the predicted cavity position I as a comparison object. Therefore, it is possible to exclude a signal that is assumed to be generated independently of the cavity 13, and thus it is possible to accurately estimate the position of the start end and the end position of the cavity 13 in the thickness direction in a shorter time.

  In the first and second experiments, the reflected wave W2b corresponding to the start position of the cavity 13 and the reflected wave W2c corresponding to the end position are combined in order to more reliably estimate the cavity thickness T. The wavelength of the electromagnetic wave W1 actually radiated from the antenna 15 in the frequency band having the stop frequency f1 to start the operation and the actual frequency from the antenna 15 in the frequency band having the stop frequency f2 where the reflected wave W2b and the reflected wave W2c interfere with each other The cavity thickness T may be calculated separately by using at least one of the wavelength of the electromagnetic wave W1 radiated to.

11 Cavity thickness estimation device
12 Road as inspection object
13 cavity
15 Antenna having the function of radiation means
16 Network analyzer with detection function
17 Computer with interpolation function
C chart I
Tr trace
W1 Electromagnetic waves that are detected waves
W2 reflected wave

Claims (8)

A cavity thickness estimation method for estimating a cavity thickness of an inspection object,
Radiating detection waves of a plurality of different frequency bands at least with respect to a predicted cavity position of the inspection object,
Detect the reflected wave of each of these detection waves,
Estimating the position of the start and end of the cavity in the thickness direction based on the difference in the reflected wave corresponding to the difference in the frequency band of the detection wave,
A cavity thickness estimation method characterized in that the cavity thickness is estimated based on the estimated start and end positions. At least for the expected cavity position of the object to be inspected, at least a plurality of frequency bands having different maximum frequencies are radiated while being swept from the minimum frequency to the maximum frequency of the frequency band,
Detect the reflected wave of each of these detection waves,
The position of the start end and the end position in the thickness direction of the cavity are estimated based on a difference in separation and synthesis states of the reflected wave corresponding to a difference in frequency band of the detection wave. Cavity thickness estimation method. Use detection waves of multiple frequency bands whose maximum frequencies are discontinuous as detection waves,
The cavity thickness estimation method according to claim 1 or 2, wherein a reflected wave corresponding to each of the detected waves is interpolated between frequency bands. The method for estimating a cavity thickness according to any one of claims 1 to 3, wherein the detection wave is emitted in a state where the detection wave is stopped at least with respect to a predicted cavity position of the inspection object. A cavity thickness estimation device for estimating a cavity thickness of an inspection object,
Radiating means for radiating detection waves of a plurality of different frequency bands to at least a predicted cavity position of the inspection object;
Detection means for detecting reflected waves of the detection waves respectively radiated from the radiation means;
Position estimating means for estimating the position of the start end and the end position in the thickness direction of the cavity based on the difference in the reflected wave corresponding to the difference in the frequency band of the detection wave emitted by the radiation means;
A cavity thickness estimation device comprising: a cavity thickness estimation means for estimating a cavity thickness based on the position of the start end and the position of the end estimated by the position estimation means. The radiating means radiates at least a detection wave of a plurality of frequency bands having different maximum frequencies from each other at least with respect to a predicted cavity position of the inspection object while sweeping from the minimum frequency to the maximum frequency of the frequency band,
The position estimation means estimates the position of the start end and the position of the end in the thickness direction of the cavity based on a difference in separation and synthesis states of the reflected wave corresponding to a difference in frequency band of the detection wave. The cavity thickness estimation apparatus according to claim 5. The radiating means uses detection waves in a plurality of frequency bands whose maximum frequencies are discontinuous as detection waves,
The cavity thickness estimation apparatus according to claim 5 or 6, further comprising interpolation means for interpolating reflected waves corresponding to each of the detected waves between frequency bands. 8. The cavity thickness estimation apparatus according to claim 5, wherein the radiation means radiates a detection wave in a state where the radiation means is stopped at least with respect to a predicted cavity position of the inspection object.