JPH1031077A - Method of detecting crack and electrode for measuring potential - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily find a crack in the ground by forming a bore hole in the ground, laying the bore hole in water flowing state, measuring the underwater potential distribution laid along the bore hole, and determining the position having a specific distribution. SOLUTION: In the ground to detect the presence of a crack 3, a bore hole 1 is formed, and water is carried into the bore hole 1. When the water permeable crack 3 is present in the middle of the bore hole 1, the tomographic state around it is changed to change the potential distribution of water, and this position is detected as the crack 3. In order to eliminate the influence of potential distribution by a difference in geological structure, the water flow in the bore hole is stopped to measure the potential distribution of stationary water. The potential distributions in water flowing and stationary states are mutually compared, whereby the crack 3 can be more precisely detected from the specific potential distribution caused in water flowing time. To measure the potential distribution, a reference electrode 21 is stopped within the bore hole 1, a probe electrode 22 is moved along the inside of the bore hole 1, and the potential in each position within the bore hole 1 is measured by a voltmeter 24.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the detection of underground permeable cracks.

[0002]

2. Description of the Related Art Conventionally, there are a method of observing a core sample of a boring and a method of measuring a hole wall resistivity of the boring hole in order to identify a crack in the boring hole. Or
A method using a float to measure the groundwater flow (see Japanese Patent Application Laid-Open No. 7-72264), or a method for investigating groundwater by a temporal change in temperature distribution (Japanese Patent Application Laid-Open No. 6-2140)
No. 45 gazette).

However, the conventional method has the following problems. <B> The presence or absence of spring water at the crack cannot be easily confirmed. <B> The device becomes large-scale.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to easily find a permeable crack in the ground.

[0005]

According to the present invention, there is provided a crack detection method for detecting a water-permeable crack in the ground, wherein a boring hole is formed in the ground, the boring hole is made to flow, and the boring hole is formed along the boring hole. Measuring the potential distribution in water, detecting the crack in the ground by finding the position in the borehole with a specific distribution of the potential distribution, a crack detection method, or a crack in the water permeability in the ground In the detection method, a boring hole is formed in the ground, the boring hole is divided into a flowing water state and a still water state, and the potential distribution in the water along the boring hole is measured for each of flowing water and still water. Then, the potential distribution between stationary water and flowing water is compared, and the potential distribution during running water is different from the potential distribution during still water, and the position in the borehole where there is a unique distribution is detected to detect cracks in the ground. Crack detection method characterized by performing Alternatively, in the crack detection method, water is injected into the boring hole, or water is discharged from the boring hole to form flowing water, or the crack detection method, or in the crack detection method, Characterized by obtaining a still water by stopping the water flow in the crack detection method, or in the crack detection method,
Crack detection characterized by placing the reference electrode and the exploration electrode in the water in the borehole, moving the exploration electrode along the borehole, and measuring the potential distribution in the water along the borehole. In a method or a potential measuring electrode for measuring a potential distribution of water flowing along a boring hole formed in the ground to detect a crack in the ground under water permeability,
A potential detection unit that detects a potential in water, and a covered cable that guides the potential from the potential detection unit to the outside of the borehole,
The potential detecting unit has an insulating container having a hole into which water enters, and has a conductor electrically connected to the coated cable in the container, and conducts the electric potential of water outside the container through the hole of the container. Characterized in that it is guided outside the boring hole through the body and the covered cable, the potential measurement electrode, or in the potential measurement electrode, characterized in that the conductor is covered with a porous body containing a saturated copper sulfate solution, The electrode for potential measurement, or the electrode for potential measurement, wherein the conductor is made of platinum or silver coated with silver chloride.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

<A> Overview of crack detection method The underground crack detection method utilizes an electrokinetic phenomenon in which a potential change occurs when water flows underground. Electrokinetic phenomena are caused by the action of an electric double layer at the interface between water and soil particles, causing the flow of water to appear as a flow of charges,
This is a phenomenon that causes a potential gradient.

In order to utilize this phenomenon for the detection of the crack 3, as shown in FIG. 1, a boring hole 1 is formed in the ground where the presence or absence of the crack 3 is to be detected, and water is caused to flow in the boring hole. If there is a water-permeable crack 3 such as a water path in the middle of the boring hole 1, the crack and the topographical state of the boring hole 1 change near the crack location, so that the potential distribution of water in the vicinity changes. By searching for the position of the change in the potential distribution, a crack can be detected.

In order to remove the influence of the potential distribution caused by other phenomena such as a difference in the geological structure from the potential distribution of the water due to the flow of the water, the flow of the water in the borehole is stopped, and the potential of the stationary water is stopped. Measure the distribution. Then, by comparing the potential distribution at the time of flowing water with the potential distribution at the time of still water, and detecting the water-permeable crack 3 from the unique potential distribution generated at the time of flowing water, the crack 3 can be detected more accurately. .

<B> Crack detection device An electrode for measuring the potential distribution of water is disposed in the borehole. The electrode may be any as long as it can measure the potential distribution of water in the borehole. For example, as shown in FIG. 1, the reference electrode 21 is kept stationary in the borehole, and the search electrode 22 is moved along the borehole. The voltmeter 24 measures the potential at each position in the borehole.

When there is a spring of groundwater in the borehole, a flow of water in the borehole can be obtained by the springwater. When there is no spring water, as shown in FIG. 2, a pipe 5 with a pump is attached to the hole, and water is injected into the boring by the pump 6 to create a flow of water in the boring.
If there is groundwater but it does not overflow, it may be pumped up by pump 6 to create a stream of water.

In order to obtain still water, in FIG. 1, a pipe with a valve 5 may be arranged at the hole, and the valve 4 may be closed to stop flowing water. When the pump 6 is used as shown in FIG. 2, the flow of water can be controlled by driving and stopping the pump 6.

The boring hole 1 is not limited to the case where it is provided below the ground, but is formed laterally from the side of a cliff, or
As shown in FIG. 3, the boring hole 1 may be formed from underground such as a tunnel 7. In this case, the boring hole 1 may be directed upward, but measurement can be performed in any direction if water can flow through the hole. In that case, groundwater may be discharged from the hose 8 or water may be supplied from the hose 8.

<C> Electrode for measuring potential Since the electrode for measuring potential measures the potential of water, it is preferable that the contact potential difference between the conductor 27 and water is small. For this purpose, a silver conductor 27 coated with silver chloride, a platinum conductor 27, or a copper conductor 27 covered with a porous body 28 containing a saturated copper sulfate solution is suitable. The porous body 28 can contain a saturated copper sulfate solution, and it is preferable that electricity flows through the conductor 27. For example, a sponge-like one or a cotton-like one can be used. By electrically connecting the insulated cable 23 to the conductor 27, the conductor 2
The potential of 7 is led to the voltmeter 24.

Since the conductor 27 preferably does not contact the wall surface of the boring, it is preferable to cover the conductor 27 with an insulating container 25. In order to make the electric potential of the conductor 27 in the insulating container equal to that of the external water, a hole 26 is formed in the container 25 so that electricity is transmitted to the conductor 27 through the hole 26.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment for detecting a permeable crack will be described below.

<A> Experiment The measurement of the permeable crack 3 is performed in a deep underground space experimental site, and the surroundings are surrounded by sedimentary soft rock. The outer diameter of the boring hole 1 was 12 cm, the opening was 50 m below the ground, and the depth was 55 m. The potential distribution was measured at 1 m intervals. The measurement is 2
The measurement was repeated twice and the measurement results were reproducible and stable.

In order to distinguish between the potential distribution caused by the flowing water and the potential distribution caused by the geological structure, a pipe 5 with a valve is attached to the bore of the borehole 1 as shown in FIG. Artificially adjust the flow of spring water, as shown in Figure 7,
Potential distribution with water flowing (potential distribution of flowing water, solid line)
And the potential distribution in the state where water is stopped (potential distribution of static water,
(Broken line) was measured, and both were compared.

As the electrode, a copper-copper sulfate electrode was used. The reference electrode 21 was arranged at the borehole, and the depth of the exploration electrode 22 was changed along the borehole 1 in order.

<B> Measurement results The measurement results are shown in the graph of FIG. From this graph, there is a clear difference in potential distribution between when water is flowing and when it is not flowing. That is, there is a potential generated by the flow of water,
And it shows that the measurement is possible.

<C> Detection of crack location From the graph of FIG. 7, in the case of running water, 35 m to 55 m from the hole
At a depth of m, a remarkable difference in the potential distribution is observed, and the peak reaches around a depth of 42 m. This peak is presumed to be a crack. The large potential change near the hole originates from the discontinuity when the water flow exits from the borehole to the ground.

In addition to the above-described potential distribution measurement, it was also confirmed from a survey of a core sample of a conventional boring and a measurement result of a hole wall resistivity as shown in FIG. 8 that a crack was present at a depth of about 42 m. Was.

[0023]

According to the present invention, the following effects can be obtained. <a> Since the potential distribution naturally generated by flowing water is measured instead of artificially applying electricity by the device, the measuring device can be simple and accurate measurement with reproducibility is possible. <B> When the potential distribution is measured both in flowing water and in still water, the potential distribution due to the stratum structure can be removed. <C> By using an electrode having a small contact potential difference, an accurate potential distribution can be measured. <D> Accurate water potential can be measured by preventing the electrode from contacting the wall surface of the borehole.

[Brief description of the drawings]

Fig. 1 Measurement diagram of the potential of water in a borehole due to spring water

FIG. 2 is a diagram showing a measurement of a potential of water in a borehole by a pump.

FIG. 3 is a diagram showing a measurement of a potential of water in a borehole in a tunnel.

FIG. 4 is a structural diagram of a copper-copper sulfate electrode.

FIG. 5 is a structural diagram of an Ag—AgCl electrode.

FIG. 6 is a structural diagram of a Pt electrode.

FIG. 7 is a diagram showing a potential distribution in a borehole.

FIG. 8: Measurement of crack by conventional hole wall resistivity measurement method

[Explanation of symbols]

 1 ··· Boring hole 21 · Reference electrode 22 · Exploration electrode 23 · Insulated cable 24 · Voltmeter 25 · Vessel 26 · Hole 27 · Conductor 28 · Porous body 3 · · Crack 4 · · Valve 5 · · Pipe 6・ ・ Pump 7 ・ ・ Tunnel 8 ・ ・ Hose

Claims (8)

[Claims] Claims: 1. A crack detection method for detecting a water-permeable crack in the ground, comprising the steps of: forming a borehole in the ground, making the inside of the borehole flow, measuring a potential distribution in water along the borehole; A crack detection method, comprising: finding a position in a borehole having a peculiar distribution in a potential distribution to detect a crack in the ground. 2. A method for detecting cracks in underground water permeability, wherein a boring hole is formed in the ground, and the boring hole is divided into a running water state and a still water state. , The potential distribution in the water along the borehole is measured, and the potential distribution between stationary water and flowing water is compared. A crack detection method, wherein a crack in the ground is detected by determining a position in the ground. 3. The crack detecting method according to claim 1, wherein water is injected into the boring hole, or water is discharged from the boring hole to form flowing water. Detection method. 4. The crack detection method according to claim 2, wherein the water flow in the borehole is stopped to obtain still water. 5. The crack detection method according to claim 1, wherein the reference electrode and the search electrode are arranged in water in the borehole, and the search electrode is moved along the borehole. A method for detecting a crack, comprising measuring a potential distribution in water along a boring hole. 6. A potential measuring electrode for measuring a potential distribution of water flowing along a boring hole formed in the ground to detect a water-permeable crack in the ground. And an insulated cable for guiding the electric potential from the electric potential detection unit to the outside of the borehole. The electric potential detection unit has an insulating container having a hole into which water enters, and is electrically connected to the insulated cable in the container. A potential measuring electrode, comprising: a conductor that has been subjected to electrical conduction; and guiding an electric potential of water outside the container from the hole of the container to the outside of the boring hole through the conductor and the coated cable. 7. The potential measurement electrode according to claim 6, wherein the conductor is covered with a porous body containing a saturated copper sulfate solution. 8. The electrode for potential measurement according to claim 6, wherein the conductor is made of platinum or silver coated with silver chloride.