JPH0933382A - Method for detecting leakage position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for detecting a leakage position in which a potential distribution showing a leakage position can be obtained only when the leakage of a water shielding sheet is detected without being influenced by a noise such as the specific resistance of an internal current electrode or waste, the construction can be executed any time without being influenced by weather conditions such as rain, and the corrosion of a potential electrode is never caused. SOLUTION: In detecting the leakage position of an electrically insulating water shielding sheet laid on a ground, a reference potential electrode 4 and a plurality of measuring potential electrodes 5... which are preliminarily wired are set under a water shielding sheet 1, an alternating direct current is generated between the internal current electrode 6 of the water shielding sheet 1 and an external current electrode 7 on the outside, and only when a potential difference exceeding a prescribed control limit value to the reference potential electrode 4 is generated in the measuring potential electrode 5, the potential distribution is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water leakage position detecting method for electrically detecting the presence or absence of water leakage and the water leakage position by laying an electrically insulating water shielding sheet at a final waste disposal site, for example.

[0002]

2. Description of the Related Art In general waste final disposal sites and control type final disposal sites, it is common practice to prevent the diffusion of harmful substances from the disposal sites by using water-blocking sheets.

However, the water-impermeable sheet has a very thin thickness of about 1.5 mm despite its high water-impervious property, so that it has deteriorated over time after completion of laying the sheet, or has a poor landfill construction. There is a case where the damage is caused by.

[0004] Therefore, conventionally, a method has been taken to detect leakage of leaching water due to functional failure such as damage to the water shielding sheet by groundwater monitoring. In this method, even if a leak is discovered, groundwater pollution is already spreading at that time, and the location of the leak cannot be identified at the time of occurrence, so the leak location cannot be repaired in real time.

For this reason, recently, a water leakage detection technique capable of accurately grasping a water leakage site has been developed, and the following two cases are representative thereof.

The first case is a method of monitoring the leakage by dividing the disposal site into small sections and dividing the drainage pipes. With this method, it is possible to detect the presence or absence of water leakage in a small section,
It cannot detect the exact location in the compartment.

In the first case, the structure of the drainage pipe becomes complicated and a high level of construction technology is required, so the number of sections is limited. That is, there is a limit to increase the detection accuracy. Therefore, it is difficult to quickly repair the leaked area.

Therefore, in recent years, in the United States EPA (Environmental Protection Agency), "Leakage detection method of water shield work by electric resistance method" (19
1982), and the second case is this development type. That is, in the electrical resistivity method, a system in which the positions and specifications of the electrodes are changed is used to electrically search for a damaged portion of the waterproof sheet.

Normally, the impermeable sheet has an electrical insulation property, so that no current flows even if a voltage is applied to the inside and outside of the disposal site, but if the impermeable sheet is damaged, it will be exposed to the outside through the damaged part. And the interior is energized. If this is indicated by the potential distribution, the damaged portion is distorted, so that the presence or absence of the damage and its position can be detected.

In the second case, although the analysis condition may be a little worse due to the environment due to the waste material and the specific resistance of the ground, once the electrodes are laid, the potential distribution is only observed after that. Maintenance is very easy. Also, in the first case, it was difficult to confirm the leakage of water by adding the work of washing the subdivided subdivisions again, but this is not the case in the second case, and in the second case it is almost impossible. Since the current situation can be grasped in real time, even if a water leak occurs, it can be immediately dealt with.

The second case is roughly divided into three methods. The first method is to install the potential electrodes on the upper part of the water shield sheet, the second method is to install the potential electrodes on the upper and lower parts of the water shield sheet, and the third method is A potential electrode is installed inside the water-blocking sheet.

[0012]

However, the above-mentioned first to third methods have the following problems.

First, since the first method employs a structure in which the potential electrode is installed in the waste material to be filled on the upper part of the water-blocking sheet, the electrode is damaged, the wiring is corroded, and the electrode Due to the occurrence of wire breakage, the need for measures against calcium adhesion and the heat generated from waste, defects will be present from the construction stage of this structure. In addition, because the potential distribution map is analyzed in wastes with various resistance values that are not uniform, the measurement values are prone to deviation due to the generation of various noises, which is caused when the electrodes are damaged at more than one point. Makes leak detection difficult.

As a concrete example, if there is no damage to the water-blocking sheet, a concentric potential distribution centering on the energization position 70 of the internal current power source can be obtained (see FIG. 7), and if there is damage, damage is made as water leak detection. A potential distribution centered on the point 80 is obtained (see FIG. 8).

However, when a sheet breakage occurs, as shown in FIG.
As shown in Fig. 3, the potential distribution centering on the energization position of the internal current power source and the potential distribution centering on the damaged part coexist, so the situation of the potential distribution becomes confusing. There is a problem that it becomes difficult.

The second method employs a structure in which the impermeable sheet is installed and the linear electrodes are installed at the same time, and the linear electrodes are installed at equal intervals above and below the impermeable sheet. . In this case, when an AC voltage is applied to the inside and outside of the repository, the conductivity above and below the water shield sheet becomes anisotropic. Therefore, use this to detect the position of water leakage by the combination of electrodes and the magnitude of the current flowing between them. Is done.

However, since the installation of the linear electrodes is carried out on-site, it is likely to be affected by weather conditions such as rainy weather, which may cause problems in construction management and process management. Further, although the detection accuracy can be down to the level of 1 cm ² at the minimum, there is a problem that it is difficult to remove noise and the like and it is difficult to maintain and manage the level.

As an example showing the third method, there is JP-A-1-178843. This adopts a structure in which sand or the like is filled between two water-impervious sheets, a large number of potential electrodes for measurement are buried therein, and a reference potential electrode is placed on the upper part of the impermeable sheet.

According to the third method, since the measuring potential electrode is installed between the two water-blocking sheets, the potential distribution is not affected by noise such as internal current electrodes and ground current, but the sheet is laid. Since it is necessary to perform the work and the work of installing the potential electrode at the same time, in this case as well, the work is carried out on site like the second method. Therefore, there is a problem that the work is easily affected by weather conditions such as rain and the work efficiency is deteriorated due to competition between the two works, which causes troubles in construction management and process management. Further, in this case, since the reference potential electrode is installed on or in the waste, there is a problem that the electrode is easily corroded by the waste.

The present invention has been made in order to solve the above-mentioned problems of the conventional example, and its purpose is to prevent water from being affected by noise such as internal current and specific resistance of wastes. A leak position detection method that can obtain the potential distribution indicating the leak position only when the sheet leak is detected, can be performed at any time without being affected by weather conditions such as rain, and does not worry about corrosion of the potential electrode. To get.

[0021]

In order to solve the above-mentioned problems and achieve the above-mentioned object, a water leakage position detecting method according to the invention of claim 1 has a reference potential electrode and a plurality of measurement potential electrodes under a water-blocking sheet. Since it is installed, it is sufficient to wire the potential electrode in advance at the factory and install this on site. Also,
A current is passed between the inside and outside of the water-blocking sheet, and the potential distribution is determined only when the potential difference between the reference potential electrode and the multiple measurement potential electrodes exceeds a predetermined control limit value. The location of water leakage can be detected in real time from the distribution.

Further, in the leakage position detecting method according to the invention of claim 2, in the invention of claim 1, since the predetermined control limit value is set to be larger than at least the noise value of the earth current or the like, it can be ignored. It is not necessary to express the potential difference (noise) even in the potential distribution.

Further, in the leakage position detecting method according to the invention of claim 3, in the invention of claim 1, at least one spare cable is provided between the reference potential electrode and each measurement potential electrode separately from the main cable. Since the cables are separated from each other, even if a trouble such as a breakage occurs in the main cable, the spare cable can be immediately substituted.

According to a fourth aspect of the present invention, in the first aspect of the present invention, a bentonite layer or a sand layer is provided below the water-blocking sheet, and a reference potential electrode and a plurality of measurement potential electrodes are provided there. Since it was buried, the potential difference is measured in a uniform soil layer that is hardly affected by noise.

Further, in the leakage position detecting method according to the invention of claim 5, in the invention of claim 1, an alternating direct current is caused to flow between the inside and the outside of the impermeable sheet to form a reference potential electrode and a plurality of measurement potential electrodes. Since a potential difference is generated between the electrodes and, it is not necessary to attach ions due to polarization near the electrodes.

[0026]

1 is a side sectional view showing a system of an embodiment of a water leakage position detecting method according to the present invention. This system focuses on the electrical insulation of the water-blocking sheet, and detects the presence or absence of water leakage and its position by obtaining the potential distribution from the current leaking from the damaged portion of the water-blocking sheet. Also,
This system is applied to the final disposal site for municipal solid waste, the final disposal site for management, etc., and it is possible to detect leaks without removing the landfill waste from the time of completion to the completion of landfill and the use of the landfill.

In FIG. 1, the water-blocking sheet 1 is laid on a soil layer 3 such as Bennite or sand, and the waste 2 is landfilled in a disposal site P formed on the inner surface of the water-blocking sheet 1. A reference potential electrode 4 and a plurality of measurement potential electrodes 5 are embedded in the soil layer 3, and the voltage (potential difference) between these potential electrodes 4 and 5 is measured.

Further, inside the disposal site P (inside the water blocking sheet 1)
An internal current electrode 6 is installed on the outside, and an external current electrode 7 is installed outside the disposal site P (outside the water blocking sheet 1). These current electrodes 6 and 7 are for detecting the currents of the potential electrodes 4 and 5. Current is sent.

Then, several groundwater monitoring wells M for carrying out water quality inspections and the like are installed outside the disposal site P and within a predetermined site boundary.

Next, a method of installing the potential electrode will be described. FIG. 2 is a configuration diagram schematically showing one example of connection between the reference potential electrode 4 and the measurement potential electrode 5.

The reference potential electrode 4 and the measurement potential electrode 5 ...
As shown in FIG. 2, they are connected by a cable, and a voltmeter 21 for measuring the voltage (potential difference) between the potential electrodes 4 and 5 and a switch box 22 for concentrating the plurality of measurement potential electrodes 5 are connected therebetween. There is. This switch box 2
2, a plurality of multi-core main cables 23 in which the measurement potential electrodes 5 are collected for each row are connected in a plurality of rows, and a spare cable 24 is connected by a similar wiring as a spare. The main cable 23 and the spare cable 24 are separated from each other at their installation locations.

Next, the procedure for installing the potential electrode will be described. The potential electrodes 4 and 5 and the cords (wires) are connected and assembled in a factory with complete waterproofing, and then brought into the field. The base for laying the water-impervious sheet 1 is sufficiently smoothed by sufficiently removing boulders and protrusions, compacting, and smoothing. A soil layer 3 such as Bennite or sand having a proper thickness is laid on the upper portion of the base, and the assembled potential electrodes 4 and 5 and the cord are installed therein. After that, the water blocking sheet 1 is laid on the soil layer 3. Further, a water leakage inspection of the water blocking sheet is performed, and a control limit value which is a threshold value for obtaining the potential distribution is set.

Here, how to obtain the potential distribution will be described. FIG. 3 is a conceptual diagram for explaining the relationship between the measurement potential electrode 5 and the potential distribution, and FIGS. 4 and 5 show the potential distribution diagram without water leakage detection and the potential distribution diagram with water leakage detection, respectively. There is.

The above-mentioned control limit value is a control voltage value that is set higher than the amount of current due to sheet damage that is negligible for environmental conditions such as earth current and water leakage detection, and this is the value for the preliminary excavation stage. It is determined based on the results of preliminary tests and water filling tests at the stage where the sheeting at the repository is completed.

An internal current electrode 6 and an external current electrode 7 are installed inside and outside the water-blocking sheet 1, respectively. Alternating direct current (rectangular wave) for periodically exchanging + and − of direct current is applied between these current electrodes 6 and 7, and this alternating direct current passes through the damaged portion of the water-blocking sheet 1 to the lower portion of the sheet to generate a reference potential. A potential difference will be generated between the electrode 4 and the measurement potential electrode 5.

If this potential difference does not exceed the control limit value, the potential distribution calculation process (potential distribution measurement) is not executed, and the potential distribution chart in which no potential distribution appears as shown in FIG.
0 is obtained.

Further, for example, when the water shield sheet 1 is damaged, a current flows from the damaged portion 31 to the soil layer 3 below the sheet as shown in FIG. 3, and the reference potential electrode 4 and the measurement potential electrode 5 ... The potential difference is detected by measuring the voltage between them. At this time, if the potential difference exceeds the control limit value, the potential distribution calculation process (potential distribution measurement) is executed, and the potential distribution centered on the damaged portion 31 is shown in FIG.
Appears at 0.

Next, the procedure of water leakage position / countermeasure repair will be described with reference to the flowchart of FIG. First, a continuity test is performed based on a preset control limit value (step 6).
01). This continuity test is preferably carried out, for example, at the end of landfilling for one day, and is carried out using alternating direct current from the internal current electrode 6 and the external current electrode 7. As a result of the measurement by the continuity test, if the potential difference between the potential electrodes 4 and 5 is equal to or less than the control limit value, it is determined that there is no water leakage (no abnormality), and the process ends. In this case, for example, as shown in FIG. 4, a potential distribution map without potential distribution measurement can be obtained. Even if there is no abnormality, for example, weekly potential distribution measurement and monthly water quality analysis (monitoring well and waste leachate) are performed (step 602).

When a potential difference exceeding the control limit value is measured in step 601, the measurement result is determined to be suspected of water leakage (abnormal), and the process proceeds to the next step 603. In this step 603, in consideration of certainty, it is expected that the management of only the control limit value will be affected by noise. Therefore, when the control limit value is exceeded, the potential distribution is measured and calculated immediately and the potential distribution is measured. Obtain the figure and check the damage to the water-blocking sheet 1 as well as the damaged position. In this case, for example, a potential distribution chart is obtained by calculation as shown in FIG.

At this time, if no abnormality (sheet damage location) can be found from the potential distribution map, it is determined as an erroneous determination (no abnormality) and the process proceeds to step 603 to investigate the cause. (Step 604).

When a leak location can be found from the potential distribution map, water quality analysis (monitoring well and waste leachate) is carried out (step 605). As a result, if the water quality is found to be abnormal, urgent measures including water-stop measures such as steel sheet piles and soil cement walls are taken because there is a possibility of groundwater contamination (step 606). Also, if there is no abnormality in water quality, it is only necessary to repair damage to the impermeable sheet 1. Therefore, for example, if the depth of accumulation of waste is shallow, excavation is performed to directly repair the damaged portion. Water is injected into the protective layer above the damaged portion of the water shield sheet 1 to take measures for preventing water leakage (step 607).

In the above embodiment, the case where one water shield sheet is laid is explained, but two water shield sheets may be laid. In this case, soil such as sand may be filled between the two water-impervious sheets, and the reference potential electrode 4 and the measurement potential electrode 5 may be installed under the second impermeable sheet from the top, As a result, the structure is the same as that of the above-mentioned embodiment except that the number of the water-blocking sheets becomes two.

The procedure shown in FIG. 6 can be automated by a computer, for example, steps 604 and 6
In 06 and 607, if data for giving guidance to the operator is stored in advance, the operator can immediately start the work without panic.

Now, as the material of the water shield sheet 1, synthetic rubber, plastic, or the like is preferable.

[0045]

As described above, according to the invention of claim 1, since the reference potential electrode and the plurality of measurement potential electrodes are installed below the water-blocking sheet, the potential electrodes are pre-wired at the factory. It is sufficient to install this on site, and it is possible to eliminate the confusing potential distribution of the internal current electrode. In addition, the electric current is passed between the inside and the outside of the waterproof sheet, and the potential distribution is obtained only when the potential difference between the reference potential electrode and the plurality of measurement potential electrodes exceeds a predetermined control limit value. The presence or absence of water leakage and its position can be detected in real time from the potential distribution. In this way, the potential distribution showing the leak position can be obtained only when the leak of the impermeable sheet is detected without being affected by noise such as the internal current electrode and the specific resistance of waste, etc. There is no influence and the construction can be performed at any time without competition between sheet construction and potential electrode installation, and there is no concern about corrosion of the potential electrode. Therefore,
It is possible to obtain a method for detecting the position of water leakage, which can provide swiftness and certainty in detecting the position of water leakage and can prevent the secondary influence on the environment due to water pollution.

According to the invention of claim 2, claim 1
In the invention, since the predetermined control limit value is set to be larger than at least the noise value such as the earth current, it is not necessary to express the potential difference (noise) to the negligible level as the potential distribution. Since the expected environmental current is ignored in advance, it is possible to obtain a highly practical water leakage position detection method.

Further, according to the invention of claim 3, in the invention of claim 1, at least one spare cable other than the main cable is wired between the reference potential electrode and each measurement potential electrode, and these are separated from each other. Therefore, even if a trouble such as disconnection occurs in the main cable, the spare cable can be immediately substituted, and therefore, the water leakage position detecting method can be obtained in which the fail-safe ability can be improved.

According to the invention of claim 4, in the invention of claim 1, a bentonite layer and a sand layer are provided below the water-blocking sheet, and the reference potential electrode and the plurality of measurement potential electrodes are embedded therein. , The potential difference can be measured in a uniform soil layer that is hardly affected by noise. Therefore, compared with the case where the potential electrode is installed on the top of the impermeable sheet, the effect of the internal current electrode and the specific resistance of the waste are It is possible to obtain a water leakage position detection method that is not affected and can reduce noise.

According to the invention of claim 5, claim 1
In the invention described above, an alternating direct current is passed between the inside and the outside of the impermeable sheet to generate a potential difference between the reference potential electrode and the plurality of measurement potential electrodes, so that ions due to polarization near the electrodes are attached. Therefore, it is possible to obtain a method for detecting a water leakage position in which an electric signal can be stably taken out and the analysis can be accurately performed.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a system of an embodiment of a water leakage position detecting method according to the present invention.

FIG. 2 is a configuration diagram schematically showing a connection example of a reference potential electrode 4 and a plurality of measurement potential electrodes.

FIG. 3 is a conceptual diagram illustrating a relationship between a measurement potential electrode and a potential distribution.

FIG. 4 is a potential distribution diagram showing a potential distribution diagram without sheet breakage according to the present invention.

FIG. 5 is a potential distribution diagram showing a potential distribution diagram when a sheet breakage occurs according to the present invention.

FIG. 6 is a flowchart illustrating a procedure of water leakage position / countermeasure repair.

FIG. 7 is a potential distribution diagram showing a potential distribution diagram when a sheet is not damaged according to a conventional example.

FIG. 8 is a potential distribution diagram showing a potential distribution diagram when a sheet breakage occurs according to a conventional example.

[Explanation of symbols]

 1 Water-impervious sheet 2 Waste 4 Reference potential electrode 5 Measurement potential electrode 6 Internal current electrode 7 External current electrode 23 Main cable 24 Spare cable

Claims (5)

[Claims] 1. A method for detecting a water leakage position of an electrically insulating water-blocking sheet according to a potential distribution, wherein a reference potential electrode and a plurality of measurement potential electrodes, which are pre-wired, are installed below the water-blocking sheet, An electric current is passed between the inside and the outside of the impermeable sheet to obtain the potential distribution only when a potential difference exceeding a predetermined control limit value occurs between the reference potential electrode and the plurality of measurement potential electrodes. A water leakage position detecting method characterized by the above. 2. The water leakage position detecting method according to claim 1, wherein the predetermined control limit value is set to be larger than at least a noise value of earth current or the like. 3. The water leakage position detecting method according to claim 1, wherein a main cable and at least one spare cable are separately provided between the reference potential electrode and each of the measurement potential electrodes. 4. Bennite is provided below the water-blocking sheet,
A soil layer such as sand is provided, and a reference potential electrode and a plurality of measurement potential electrodes are embedded in the soil layer.
The leak detection method described. 5. When the electric current is passed between the inside and the outside of the impermeable sheet, current electrodes are respectively installed inside and outside the impermeable sheet, and alternating + and − of DC are exchanged periodically. The leak position detecting method according to claim 1, wherein a direct current is applied.