JP2009025103A - Reflection method survey system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly-versatile reflection method survey system capable of enlarging vibration energy of a vibration source, simultaneously adjusting its frequency, and switching freely a longitudinal wave to/from a transversal wave, in reflection method survey capable of surveying a buried object and a stratum structure in an underground shallow part easily from the ground surface. <P>SOLUTION: This reflection method survey system 100 is equipped with a magnetostrictive oscillator 110 installed on the ground surface, for generating a transversal wave by a magnetostrictive element to the underground; a detector 120 for detecting a reflected wave reflected by an underground buried object or a stratum boundary and reaching the ground surface; and a position estimation device 130 for estimating the position of the buried object or the stratum boundary by the detected reflected wave. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a reflection method exploration system for exploring buried objects and strata structures in the underground using a reflection method.

  Conventionally, reflection method exploration has been used in which a buried object buried in the ground is estimated nondestructively without digging up the ground. This is a technique for oscillating an elastic wave with physical vibration toward the ground and estimating the position of the buried object through a reflected wave from the buried object.

As a source of such reflection method exploration, underground exploration using sound waves, hammering, dynamite, blasting by a shaker, and the like has been carried out. Moreover, in the exploration device used in the hole, use of a piezoelectric element or a magnetostrictive element has been studied (for example, Patent Document 1). Furthermore, when high-precision exploration is required, a technique has been devised for exploring shallow underground portions (the actual measurement depth is generally about 2 m) using an electromagnetic wave radar.
JP 10-319132 A

  However, in the case of reflection method exploration using sound waves as described above, it is difficult to apply to soft ground or unsaturated ground with low vibration energy. At this time, if the frequency of the sound wave is set low, it can be applied to soft ground, but the exploration accuracy is lowered, and there is a problem that the buried object or the formation boundary cannot be accurately estimated. Furthermore, due to the characteristics of sound waves, only longitudinal waves (P waves) can oscillate with respect to the ground. Longitudinal waves have characteristics such as high transmission speed, but have a high energy decay rate and a problem that a desired level of reflected waves cannot be obtained.

  In addition, when seismic waves such as hammer hits are used, the vibration energy can be increased and the exploration area can be expanded, but since the frequency is low and it cannot be set to an arbitrary frequency, the rough underground It could only be used for exploration of complex geological structures.

  Furthermore, the above-described technique using a piezoelectric element or a magnetostrictive element for exploration in a hole requires drilling of the exploration hole and a preliminary investigation of the drilling hole, and has led to an increase in exploration cost and exploration period. In addition, the size of the source is limited due to the spatial constraints of the exploration hole, and there is a problem that the strength of the source cannot be increased. In some cases, the survey cannot be performed depending on the geology and the distance to the object. In addition, special considerations were necessary to oscillate elastic waves from inside the hole (for example, water inside the hole is necessary to oscillate P waves, and to oscillate S waves. It is necessary to make the oscillator adhere to the hole wall with high rigidity). Such technology does not suggest application to reflection method exploration in which exploration is easily performed from the ground surface without digging up the ground.

  In addition, subsurface exploration using electromagnetic wave radar has high resolution and high accuracy, but it contains a lot of noise due to its energy constraints, and the waveform is deformed due to the influence of salt water with a high dielectric constant and metal that is a conductor. As a result, the exploration results are greatly distorted by salt water and metal objects. Therefore, there is a problem that it cannot be used for exploration of a beach area having a low ground resistivity. In addition, the exploration results are greatly distorted by the influence of metal structures such as guardrails and radio wave devices such as mobile phones.

  The present invention has been made in view of the above-mentioned problems of conventional buried object exploration, and the object of the present invention is to provide a reflection method exploration method for easily exploring buried objects in the underground from the ground surface. It is to provide a highly versatile reflection probing system that can adjust the frequency while increasing the vibration energy of a source and can freely switch between longitudinal and transverse waves.

  In order to solve the above-described problems, according to one aspect of the present invention, there is provided a reflection method exploration system for exploring a buried object and a geological structure in the underground using a reflection method, A magnetostrictive oscillator that generates vibration by a magnetostrictive element, a detector that detects a reflected wave that reaches the ground surface after being reflected at the buried object or formation boundary, and a position of the buried object or formation boundary by the detected reflected wave And a position estimation device for estimating the reflection method.

  The present invention is characterized in that a magnetostrictive element is applied to a reflection method exploration in which a buried object at a depth of 0 to 100 m can be easily explored from the ground surface. A magnetostrictive element can vibrate with high energy and has a long stroke as compared with a sound wave or a piezoelectric element. Therefore, the position of the buried object can be reliably estimated even on soft ground or unsaturated ground.

  Further, the magnetostrictive element can be vibrated at a higher frequency than that of seismic waves or the like. High-frequency elastic waves (especially transverse waves) not only have high resolution, but also have high directivity, so that they are less diffused. Therefore, even when the buried object is small, the position can be specified with high accuracy. In addition, unlike a sound wave or the like, an individual medium can be directly vibrated, so that a longitudinal wave and a transverse wave can be freely switched by changing the installation state.

  In addition, this configuration, which explores buried objects and strata in the underground from the ground surface, eliminates the need for drilling drill holes and preliminary surveys for drilling, greatly reducing exploration costs and exploration time. Is possible. In addition, since there is no spatial restriction on such a ground surface, unlike the exploration hole, the size of the vibration source can be freely selected. For example, the magnetostrictive elements can be enlarged or juxtaposed. It is possible to increase the strength of the vibration. Further, unlike the case where an elastic wave is oscillated from the inside of the hole, special considerations such as the presence of water in the hole and the adhesion of the oscillator are unnecessary, and the exploration can be easily performed.

  The magnetostrictive oscillator may include a ground surface contact portion that is in surface contact with the ground, and a magnetostrictive element having an end in the vibration direction fixed to the ground surface contact portion. Further, the contact area of the ground surface contact portion with the ground surface may be set based on the size and depth of the buried object or the stratum boundary, the size, the number, the amplitude, and the frequency of the magnetostrictive oscillator.

  By fixing the end of the magnetostrictive element to the ground surface contact portion, the vibration of the magnetostrictive element can be transmitted to the ground surface contact portion. In addition, since the directivity of elastic wave transmission can be adjusted according to the size of the contact area, the contact area is set based on the size and depth of the buried object, and high-precision underground exploration according to the object Is possible.

  The ground surface contact portion may be a part of a protective case containing the magnetostrictive element. With such a configuration, the portability and storage property of the magnetostrictive oscillator can be improved, and the magnetostrictive element can be waterproofed and dustproof, so that the reflection method exploration system can be operated even in some adverse environments such as rain. .

  The magnetostrictive oscillator can arbitrarily change the vibration frequency, and the position estimation device can estimate the position by sweeping the frequency of the magnetostrictive oscillator and selecting an optimum frequency.

  In the present invention, a configuration in which the vibration frequency of the magnetostrictive oscillator is arbitrarily set is used, and the frequency is shifted, and the frequency at which the measurement sensitivity becomes high (the vibration receiving level becomes high overall) can be derived. Therefore, it is possible to obtain a highly accurate and stable measurement result regardless of the ground conditions such as specific resistance.

  The search of the buried object or the stratum structure by the reflection method search system may be performed a plurality of times under the same conditions, and the position estimation device may estimate the position based on the average value of the plurality of measurements.

  Although a desired measurement signal and noise are mixed in one measurement, the measurement signal has repeatability, and noise has no repeatability. Therefore, by superimposing and averaging a plurality of measurements, noise can be canceled and the signal can be amplified, and only the measurement signal can be extracted accurately.

  In the reflection method exploration system of the present invention, a buried object in the underground can be easily explored from the ground surface with high vibration energy and high frequency. Further, the frequency can be arbitrarily adjusted, and the longitudinal wave and the transverse wave can be switched freely. Therefore, it is possible to reliably extract the buried object under the optimum conditions regardless of the ground state to be measured.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  Usually, vibration energy and frequency are in a trade-off relationship. For example, seismic waves having high energy such as vibrators, hammer hits, dynamite, and blasting by a shaker have a low frequency, and sound waves having a high frequency have a low energy. Therefore, in the reflection method exploration system, a high energy source and a high frequency source are properly used depending on the application. The present embodiment provides a highly versatile reflection survey system that achieves high energy and high frequency at the same time, and can change the frequency and switch between longitudinal and transverse waves.

  FIG. 1 is a longitudinal sectional view for explaining each component of the reflection method exploration system 100 in the present embodiment. The reflection method exploration system 100 of FIG. 1 includes a magnetostrictive oscillator 110, a detector 120, and a position estimation device 130. In the present embodiment, the position of the buried object or the stratum boundary is estimated, but in order to facilitate understanding, hereinafter, it is simply abbreviated as a buried object. Therefore, the place to be buried includes the stratum boundary in the stratum structure exploration.

  Further, in this embodiment, since the buried object and the stratum structure are explored from the ground surface, drilling of the exploration hole and preliminary investigation for the drilling are unnecessary, and exploration costs and exploration are not necessary. Significant time savings are possible. Furthermore, since there is no spatial restriction on such a ground surface, unlike the exploration hole, the size of the vibration source can be freely selected. For example, the magnetostrictive element described in detail below can be enlarged. It is possible to increase the strength of the vibration by juxtaposing a plurality. Further, unlike the case where an elastic wave is oscillated from the inside of the hole, special considerations such as the presence of water in the hole and the adhesion of the oscillator are unnecessary, and the exploration can be easily performed.

  The magnetostrictive oscillator 110 includes a magnetostrictive element 112, a ground surface contact portion 114, and a protective case 116. The magnetostrictive oscillator 110 is installed on the ground, vibrates the magnetostrictive element 112, and, for example, a transverse wave against the ground. 140 (S wave) is generated.

  The present embodiment is characterized in that the magnetostrictive element 112 having excellent vibration performance is applied to a reflection method exploration in which a buried object and a stratum structure in a depth of 0 to 100 m can be easily explored from the ground surface. The magnetostrictive element 112 is a material that converts a voltage change into a volume change in one direction using a phenomenon that causes deformation according to the magnitude of the ferromagnetic material that constitutes the magnetostrictive element 112. Among them, the giant magnetostrictive material used in the present embodiment has characteristics that the displacement rate is large and the response speed is fast.

  The magnetostrictive element 112 can vibrate with higher energy than a sound wave or piezoelectric element used for reflection method exploration, and its stroke 142 (about 0.1 mm) is 10 to 50 times or more that of the piezoelectric element. . Therefore, even if the target ground is soft ground or unsaturated ground, the vibration energy can be reliably transmitted to the buried object 144, and the preliminary investigation on the possibility of underground exploration becomes unnecessary.

  The magnetostrictive element 112 is not limited to a high energy output, and the vibration frequency thereof can be arbitrarily set, and can vibrate at a higher frequency than that of the seismic wave. As such a magnetostrictive element, for example, when “V2Xπ20 (product name)” manufactured by TDK Corporation is used, a vibration frequency of 50 Hz to 20 kHz can be obtained.

  In general, when the vibration frequency is low, elastic waves are transmitted through a buried object for exploration, and a reflected wave cannot be obtained. Further, when the vibration frequency is high, the elastic wave is attenuated and does not reach the embedded object, and even if it reaches the embedded object, the reflected wave is also attenuated, so that it is difficult to obtain a good measurement result.

  In the reflection method exploration system 100, the higher the frequency, the higher the accuracy and the smaller the buried object can be detected. Here, since the high-frequency transverse wave output from the magnetostrictive oscillator 110 has high directivity and little diffusion, it is particularly suitable for exploring a shallow buried object 144. However, when the frequency is high, the wavelength is shortened and the arrival rate of the elastic wave is deteriorated, so that the measurable range is narrowed. Therefore, the frequency should be determined in consideration of the measurement depth.

  Furthermore, since the vibration frequency of the magnetostrictive element 112 can be arbitrarily changed, the position estimation device 130 described later sweeps the frequency of the magnetostrictive oscillator 110 and selects an optimum (high sensitivity) frequency to estimate the position. be able to. For example, when the ground becomes soft, the waveform transmission speed v decreases, and the wavelength λ decreases even at the same frequency. At this time, based on the wavelength λ = v / f, the vibration frequency f (Hz) is changed in accordance with the change of the waveform transmission speed v, so that it is optimum even for soft ground or unsaturated ground with a low waveform transmission speed v. It is possible to maintain a large wavelength λ. Therefore, a highly accurate and stable measurement result can be obtained.

  The ground surface contact portion 114 is in surface contact with the ground surface while fixing and supporting the end portion of the magnetostrictive element 112 described above. Here, the contact area is increased by laying the magnetostrictive oscillator 110 itself in the ground and filling the lower portion.

  FIG. 2 is an explanatory diagram for explaining a structure for fixing the magnetostrictive element 112 to the ground surface contact portion 114. The expansion and contraction of the magnetostrictive element 112 is limited simply by installing the magnetostrictive element 112 on the inner surface of the ground surface contact portion 114, and the vibration is not sufficiently transmitted to the ground surface contact portion 114. As shown in FIG. 2, the vibration of the magnetostrictive element 112 can be efficiently transmitted to the ground surface contact portion 114 by fixing the end of the magnetostrictive element 112 to the surface 114b perpendicular to the main surface 114a of the ground surface contact portion 114. it can.

  The contact area of the ground surface contact portion 114 with the ground surface may be set based on the size and depth of the buried object (or the stratum boundary), the size, the number, the amplitude, and the frequency of the magnetostrictive oscillator. Moreover, since the directivity of elastic wave transmission can be adjusted by the size of the contact area, the contact area is set based on the size and depth of the buried object 144, and the underground with high accuracy according to the object. Exploration becomes possible. In the soft ground, which is one of the objects of this embodiment, elastic waves are easily attenuated, so it is particularly important to increase directivity.

  When it is desired to increase the vibration energy while keeping the contact area of the ground surface contact portion 114 with the ground surface constant, a large element can be used as the magnetostrictive element 112, but a plurality of parallel arrangements can also be used. In this case, the plurality of magnetostrictive elements 112 are arranged accurately in parallel with the same polarity, and signals having the same phase are applied.

  The protective case 116 is formed in various shapes such as a rectangular shape and a flat plate shape in addition to the columnar shape shown in FIG. 2, and includes the magnetostrictive element 112 for protection. At this time, the ground surface contact portion 114 also forms a part of the protective case 116. With this configuration, the portability and storage property of the magnetostrictive oscillator 110 can be improved, and the magnetostrictive element 112 can be waterproofed and dustproof. Therefore, the reflection method exploration system 100 can be operated even in some adverse environments such as rain. be able to.

  The detector 120 detects the reflected wave 146 that has been reflected by the underground buried object 144 (or the stratum boundary) and reached the ground surface.

  The position estimation device 130 is composed of a computer including a central processing unit (CPU), and estimates the position of the buried object 144 (or the formation boundary) based on the detected reflected wave 146.

  Moreover, the position estimation apparatus 130 can perform the search of the buried object (or the stratum structure) by the reflection method search system 100 a plurality of times under the same conditions, and can estimate the position from the average value of the plurality of measurements. Although a desired measurement signal and noise are mixed in one measurement, the measurement signal has repeatability, and noise has no repeatability. Therefore, by superimposing and averaging a plurality of measurements, noise can be canceled and the signal can be amplified, and only the measurement signal can be extracted accurately.

  Next, a specific exploration method using the reflection method exploration system 100 described above will be described.

  FIG. 3 is an explanatory view showing an installation example of the reflection method exploration system 100. 3A shows a plan view when the ground surface is viewed from above, and FIG. 3B shows a longitudinal sectional view for representing vibration transmission to the underground.

  The magnetostrictive element 112 according to the present embodiment can directly vibrate an individual medium, unlike sound waves, etc., so that the installation state of the magnetostrictive oscillator 110 can be changed to vertical or horizontal to freely switch between vertical and horizontal waves. Can do. Therefore, both longitudinal waves (P waves) and transverse waves (S waves) can be used.

  For example, when performing reflection method exploration using longitudinal waves, the magnetostrictive oscillator 110 is installed perpendicularly to the ground surface 150 as shown by the wavy line in FIG. 3B to generate vibration perpendicular to the ground. Further, when performing reflection method exploration using a transverse wave, as indicated by the solid line in FIG. 3B, the magnetostrictive oscillator 110 is installed or buried horizontally to generate vibration parallel to the ground.

  Longitudinal waves are also referred to as sparse and dense waves, and have a high transmission speed but poor directivity, tend to diffuse at a wide angle from the source, and are easy to dissipate. Compared with the longitudinal wave, the transverse wave has high directivity and is difficult to dissipate, so that the vibration easily reaches the buried object, and a stable measurement result can be obtained. Moreover, since directivity can be maintained even if the frequency is increased, underground exploration can be performed on the kHz order.

  Moreover, in the plan view of FIG. 3A, two installation examples for generating a transverse wave are shown. Conventionally, as shown by the dotted line in FIG. 3A, the magnetostrictive oscillator 110 is installed in a direction orthogonal to the direction in which the detector 120 is installed, and vibrates in the longitudinal direction thereof. This is because when the detector 120 vibrates in the direction in which it is installed, the resistance increases by the detector 120, and the longitudinal wave directly affects the detector 120, and a desired detection result cannot be obtained. It was because it was thought.

  However, by repeating the experiment, a better experimental result is obtained when the magnetostrictive oscillator 110 is directed away from the conventional device, that is, toward the detector 120 as shown by the solid line in FIG. I understood that. When this phenomenon is examined in detail, the longitudinal wave transmitted through the ground surface, which was thought to directly affect the detector 120, is attenuated (dissipated) during transmission, and the detector 120 is substantially affected. It turned out not to give. Therefore, the buried object 144 can be detected with higher accuracy by directing the magnetostrictive oscillator 110 toward the detector 120.

  Conventionally, in order to avoid the influence of the transverse wave, the distance between the magnetostrictive oscillator 110 and the detector 120 is large. However, in the arrangement in which the magnetostrictive oscillator 110 is directed to the detector 120, the influence of the longitudinal wave is small. The distance can be significantly shortened. For example, in the reflection method exploration system 100 of the present embodiment, good test results could be obtained even when the magnetostrictive oscillator 110 and the detector 120 were brought closer to each other by about 50 cm. Below, the measurement result regarding three installation of the magnetostriction oscillator 110 mentioned above is compared.

  FIG. 4 is a diagram showing the measurement result of the embedded object 144 according to the installation state of the magnetostrictive oscillator 110. FIG. 4A shows an exploration result when the magnetostrictive oscillator 110 is installed perpendicularly to the ground surface 150 and a longitudinal wave is applied, and FIG. 4B is a transverse wave installed in a direction orthogonal to the detector 120. FIG. 4C shows a search result when adding a transverse wave by installing in the direction of the detector. The target buried object is assumed to have a depth of about 3 m.

  In FIG. 4A, the amplitude of the vibration radiated into the ground is attenuated, and the reflected wave is hardly obtained, only the surface wave 200 is detected, and the buried object cannot be identified. In FIG. 4B, there is a point 202 that seems to be a buried pipe, and it may be specified if the existence of the buried object is known. However, the energy of the transverse wave that travels on the ground surface is too strong, and the measurement result is the surface wave 200. The result was buried in. Compared with these two cases, surface waves are hardly detected in FIG. 4 (c), and the buried object, the buried pipe 210 provided in the shallow portion of the ground and the water tank bottom plate 212 provided in the deep portion are also detected. ing. From this result, it is possible to understand the high accuracy when installed in the direction of the detector 120.

  Here, the reason why the detectors 120 are symmetrically arranged on both sides of the magnetostrictive oscillator 110 is that if they are biased to one side, the reflection path becomes longer and the detection accuracy is lowered. By arranging, the reflected wave can be detected efficiently.

  Further, in the actual reflection method exploration, the magnetostrictive oscillator 110 is installed at a plurality of locations, and a plurality of detection signals of the detector 120 are acquired for each. Therefore, while maintaining the positional relationship between the magnetostrictive oscillator 110 and the detector 120, all the combinations are shifted by the moving means.

  In the reflection method exploration system 100 as described above, the buried object in the underground can be easily explored from the ground surface with high vibration energy and high frequency. Further, the frequency can be arbitrarily adjusted, and the longitudinal wave and the transverse wave can be switched freely. Therefore, it is possible to reliably extract the buried object under the optimum conditions regardless of the ground state to be measured.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  INDUSTRIAL APPLICABILITY The present invention can be used for a reflection method exploration system for exploring buried objects and strata structures in the underground using a reflection method.

It is a longitudinal cross-sectional view for demonstrating each component of a reflection method exploration system. It is explanatory drawing for demonstrating the fixation structure to the ground surface contact part of a magnetostriction element. It is explanatory drawing which showed the example of installation of the reflection method search system. It is the figure which showed the measurement result of the embedded object by the installation state of a magnetostriction oscillator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Reflection method exploration system 110 ... Magnetostrictive oscillator 112 ... Magnetostrictive element 114 ... Ground surface contact part 116 ... Protective case 120 ... Detector 130 ... Position estimation apparatus

Claims (6)

A reflection method exploration system for exploring buried objects and formations in the underground using a reflection method,
A magnetostrictive oscillator that is installed on the ground surface and generates vibration from the magnetostrictive element in the ground;
A detector that detects a reflected wave that reaches the surface of the earth after being reflected at a buried object or stratum boundary;
A position estimation device that estimates the position of the buried object or the boundary of the formation by the detected reflected wave;
A reflection survey system characterized by comprising:   2. The magnetostrictive oscillator according to claim 1, wherein the magnetostrictive oscillator includes a ground surface contact portion that is in contact with the ground surface, and a magnetostrictive element having an end portion in a vibration direction fixed to the ground surface contact portion. Reflection survey system.   The contact area with the ground surface of the ground surface contact portion is set based on the size of the buried object and the boundary of the formation and its depth, the size, number, amplitude and frequency of the magnetostrictive oscillator, The reflection method exploration system according to claim 2.   The reflection method exploration system according to claim 2 or 3, wherein the ground surface contact portion is a part of a protective case containing the magnetostrictive element.   The reflection method exploration system according to any one of claims 1 to 4, wherein the position estimation device sweeps the vibration frequency of the magnetostrictive oscillator and selects an optimum frequency to estimate the position. Exploration of buried objects or strata boundaries by the reflection method is performed multiple times under the same conditions.
The reflection method exploration system according to claim 1, wherein the position estimation device estimates a position based on an average value of a plurality of measurements.

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