JP2014157037A - Magnetic prospecting method for metallic elongate member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic prospecting method for a metallic elongate member capable of accurately performing magnetic survey of an embedded state of an elongate member such as an earth anchor.SOLUTION: Disclosed is a magnetic prospecting method for a metallic elongate member in which, out of the metallic elongate member 1 (earth anchor) which is embedded in the underground G and left therein, a head part 1a exposed onto the ground is made to pass through a conductive coil 2, the conductive coil 2 is energized to intensify the disturbance of a magnetic field from the elongate member 1, and an embedded state of the elongate member 1 is searched by a magnetic searcher 4.

Description

  The present invention relates to a magnetic exploration method for an elongated metal member such as an earth anchor.

  A metal elongated member made of a tie rod or the like is generally applied as a ground anchor as a retaining work for a mountain stop. And avoid the earth anchor when the ground improvement work or the construction of a new structure (semi-underground building, station building, underground tunnel, etc.) is performed on the ground where the earth anchor is already buried in the ground. Need to be installed. In addition, there are pipes (steel pipes, etc.), steel pipe piles, etc. that have been used as infrastructure equipment as structures already buried in the ground.

  Although the burial state and burial position of such earth anchors and steel pipe piles can be roughly confirmed with the design drawings used in the construction in which they are constructed, they cannot always be precisely identified from the design drawings etc. Absent.

  Here, the “embedding state” means information such as the length of the earth anchor and its three-dimensional embedding angle when the object to be buried is an earth anchor, for example.

  When such underground objects are made of metal, a magnetic probe such as a magnetic sensor is used, and the metal magnetic material in the ground is magnetized in the length direction. Thus, a method of detecting the magnetization intensity of a magnetic substance in the ground is generally applied.

  For example, if the volume of a metal magnetic material buried in the ground is large to some extent, such as large-diameter steel pipes applied in infrastructure facilities and piles, the magnetic field generated from the magnetic material is greatly disturbed, The buried state can be identified with a certain degree of accuracy by magnetic exploration.

  However, since the above-mentioned earth anchors and the like have a relatively small cross section, the disturbance of the magnetic field generated is small, so that the earth anchors existing in the ground can be accurately identified from the ground with a magnetic probe. It is extremely difficult.

  In view of this, the following two magnetic field strengthening methods can be cited as measures for easily identifying the embedded state by strengthening the magnetic field of the earth anchor having a small magnetic field disturbance.

  One of the magnetic field enhancement methods is a method of strengthening the magnetic field of the earth anchor by installing a strong permanent magnet on the head of the earth anchor. Permanent magnets that are currently commercially available and easy to obtain include ferrite magnets, alnico magnets, neodymium magnets, etc., among them, because the maximum energy product is the largest and the most powerful magnet is a neodymium magnet, By installing this neodymium magnet on the head of the magnetic probe, the magnetic quantity of the object to be searched can be effectively increased.

  However, in this magnetic field enhancement method, since the magnetic force of the magnet is strong, it is necessary to be careful in handling the magnet itself, and further, there is a problem that a magnetic amount exceeding the magnetic amount of the magnet cannot be expected.

  On the other hand, the other one of the magnetic field enhancement methods is a method of generating a magnetic field in the earth anchor by passing a current directly through the earth anchor. When a current is passed through a conductor such as an earth anchor, a magnetic field is generated. Therefore, there is a possibility that a magnetic field is directly generated from the earth anchor by flowing a current through the earth anchor itself to be searched and the generated magnetic field can be detected. Since the strength of the magnetic field depends on the magnitude of the current, it is necessary to pass a large current.

  However, in this magnetic field strengthening method, there is a possibility that the current that can be expected to be effective does not flow when the surrounding soil where the earth anchor is present has a high specific resistance, and further, the far electrode for flowing the current There is a problem that it is necessary to install.

  Patent Document 1 relates to a magnetic exploration method for magnetic exploration of whether or not a gas / water pipe is buried, and a method for magnetizing the gas / water pipe from the ground surface with an exciting coil and measuring the magnetic field distribution. It is disclosed.

  However, since this method magnetizes the embedded object with the ground excitation coil, the effect of strengthening the magnetic field is small, and the elongated object such as an earth anchor is not the target. In this case, it is difficult to accurately identify the buried state.

JP 11-295437 A

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a magnetic exploration method for a metal elongated member capable of accurately magnetically exploring the embedded state of an elongated member such as an earth anchor. .

  In order to achieve the above-mentioned object, the method for magnetic exploration of a metal elongated member according to the present invention includes a conductive coil formed on the head exposed to the ground among the metal elongated members embedded and left in the ground. In this case, the conductive coil is energized to increase the disturbance of the magnetic field from the elongated member, and the embedded state of the elongated member is probed by a magnetic probe.

  In the magnetic exploration method of the present invention, the magnetic exploration target has a relatively small cross-sectional area such as a reinforcing bar (different diameter, round bar) including a tie rod, PC steel bar, PC steel wire, PC steel wire, etc., and therefore its own magnetic field. This is a metal elongated member with a small disturbance.

  Rather than a method of directly passing an electric current or installing a permanent magnet to such a metal elongated member, in the present invention, the elongated member is formed by passing the conductive coil through the head of the elongated member and energizing the conductive coil. Is used as an iron core in a coil constituting an electromagnet to increase the magnetic strength.

  By energizing the conductive coil to increase the disturbance of the magnetic field from the elongated member and exploring the embedded state of the elongated member with a magnetic probe, the embedded state of the elongated member, that is, the length of the elongated member and its three-dimensional It is possible to accurately identify a typical embedding angle, the three-dimensional position of the tip of the elongated member, and the like.

  Magnetic exploration using a magnetic probe includes a method of moving the magnetic probe on the ground and a method of drilling a measurement borehole in a vertical, horizontal, or inclined method and dropping the magnetic probe into it. However, by applying the magnetic exploration method of the present invention, it is possible to increase the disturbance of the magnetic field even for an elongated member having a small cross section, and the embedded state of the elongated member with high accuracy while running the magnetic probe on the ground. Can be specified.

  In particular, since the magnetic strength of an electromagnet is proportional to the number of turns and current value per unit length of a conductive coil, the magnetic strength desired to be generated can be set by appropriately adjusting either or both of the number of turns of the coil and the current value. Can be easily obtained.

  In addition, it is a simple exploration method in which a conducting coil is temporarily fixed by passing it through the head of an elongated member, and then the magnetic exploration is performed by energizing the conductive coil. Even when there are restrictions on the exploration, such as, the magnetic exploration can be executed efficiently.

  As can be understood from the above description, according to the magnetic exploration method of the metal elongated member of the present invention, the conductive coil is passed through the head of the metal elongated member embedded and left in the ground, By conducting the magnetic exploration by energizing the conductive coil and increasing the disturbance of the magnetic field from the elongated member, the embedded state of the elongated member can be identified efficiently and accurately.

It is a flowchart explaining the magnetic exploration method of this invention. FIG. 2 is a flowchart illustrating a magnetic exploration method following FIG. 1. It is a figure which shows the result of having measured the disorder of the magnetic field by changing the presence or absence of a magnetic body and the separation to a magnetic body.

  Hereinafter, an embodiment of a magnetic exploration method for a metal elongated member according to the present invention will be described with reference to the drawings. In addition, although the example of illustration specifies the embedment state of the earth anchor applied as a construction work of a retaining wall, in addition to the example of illustration, various forms of metal elongated members are various in the ground. It goes without saying that the magnetic exploration method of the present invention can be applied to the identification of the embedded state embedded in the form (the state embedded in the vertical direction, the state embedded in the horizontal direction, etc.).

(Embodiment of magnetic exploration method for metal elongated member)
1 and 2 are flowcharts illustrating the magnetic exploration method of the present invention in that order.

  As shown in the drawing, the ground G is supported by a concrete or steel retaining wall D that extends in the vertical direction, and the ground G through the retaining wall D with the earth anchor 1 refraining from the earth anchor 1 as a back-up work. Is supported.

  For example, in constructing a structure such as a building or a station building above the ground G, when constructing a support pile for supporting the structure in the ground G, an earth anchor 1 extending obliquely in the underground G is provided. It is necessary to avoid construction.

  Therefore, by utilizing the fact that the earth anchor 1 (magnetic material) in the ground G is magnetized in the length direction, the magnetization strength of the earth anchor 1 is detected and the embedded state, that is, the earth anchor 1 A magnetic exploration method that identifies the length, three-dimensional embedding angle, three-dimensional position of the tip, etc. is executed.

  In carrying out this magnetic exploration method, the earth anchor 1 made of a PC steel material such as a wire rather than a PC steel has a small cross section and a small magnetic strength and magnetic field disturbance. For this reason, it is difficult to accurately identify the buried state of the earth anchor 1 by magnetic exploration.

  Therefore, first, as shown in FIG. 1, the conductive coil 2 is passed through the head 1a of the earth anchor 1 (X direction), and the conductive coil 2 is temporarily attached to the head 1a of the earth anchor 1 as shown in FIG. The conductive coil 2 is connected to the power supply circuit 3 and energized.

  The earth anchor 1 that originally had a small disturbance of the magnetic field is energized to the conductive coil 3 so that the earth anchor 1 acts as an iron core in the coil constituting the electromagnet, and the magnetic field MF of the earth anchor 1 itself. The intensity of the magnetic field increases and the disturbance of the magnetic field also increases.

  At the stage where the disturbance of the magnetic field of the earth anchor 1 becomes large, the earth anchor 1 is detected by running the magnetic probe 4 on the surface of the retaining wall D (Y direction) and detecting the disturbance of the magnetic field emitted from the earth anchor 1. Can be accurately identified.

  According to the magnetic exploration method shown in the figure, even if an earth anchor has a small cross section and a small magnetic field disturbance, the embedded state can be accurately and easily simplified by forcibly increasing magnetism using the conductive coil 2. Can be identified in a simple way. Further, according to the illustrated magnetic exploration method, since the magnetic strength of the electromagnet is proportional to the number of turns and current per unit length of the conductive coil, either or both of the number of turns and the current value of the conductive coil 2 are appropriately set. By adjusting, it is possible to easily obtain the magnetic intensity desired to be generated.

[Experiment to verify whether magnetic quantity depends on the size of metallic magnetic material, etc. and its results]
The present inventors conducted various experiments shown below in order to verify whether or not the amount of magnetism depends on the size of a metallic magnetic material. Specifically, it is a calibration test of a magnetic probe (MB101 manufactured by Shimadzu Corporation), a structure penetration investigation, and a survey of underground objects.

(Magnetic probe calibration test)
A single-pipe pipe cut to a length of 1.0 m was installed in a place not affected by other magnetic materials, and the separation distance was measured at two positions of 0.5 m and 1.0 m. The measurement results are shown in FIG.

  From FIG. 3, it was found that the magnetic quantity of a 1.0 m single pipe was about 3.0 μT at a distance of 0.50 m and about 1.0 μT at a distance of 1.00 m.

(Investigation of underground objects using horizontal boring holes)
From the position and direction of horizontal boring and the plot of the position of the survey hole on the plan view, a 200mm x 200mm H-section steel was built as a pile near the survey hole (the shortest separation distances 0.15m and 0.30m). It was found that the magnetic quantity detected at this time was about 40 μT at a distance of 0.15 m and about 20 μT at a distance of 0.30 m.

(Investigation of steel pipe pile penetration depth by vertical magnetic survey)
A vertical magnetic survey was conducted to understand the depth of steel pipe pile penetration. The distance between the steel pipe pile and the measurement hole is 0.60m, and the diameter of the steel pipe pile is 600mm. As a result of the exploration, a maximum response of 10μT was shown near the bottom of the pile.

(Comprehensive findings)
From the above three types of experimental results, it can be concluded that the amount of magnetism depends on the size of the metal magnetic material.

  That is, since the magnetic quantity is small in a small cross-section magnetic material such as an earth anchor, the embedded state can be accurately and easily specified by applying the magnetic exploration method of the present invention.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Elongated member (earth anchor), 1a ... Head, 2 ... Conductive coil, 3 ... Power supply circuit, 4 ... Magnetic probe, G ... Underground (ground), D ... Mountain retaining wall, MF ... Magnetic field

Claims (3)

Among the metal elongated members that are buried and left in the ground, the conductive coil is passed through the head exposed on the ground,
A magnetic elongate member magnetic exploration method in which a conductive coil is energized to increase a magnetic field disturbance from an elongate member, and an embedded state of the elongated member is explored by a magnetic probe.   The magnetic exploration method for a metal elongated member according to claim 1, wherein the buried state of the metal elongated member is explored by a magnetic probe on the ground.   The magnetic elongate member magnetic exploration method according to claim 1 or 2, wherein the metal elongate member is an earth anchor that is a construction for retaining a mountain.

Images