JP2002031579A - Method for obtaining resistivity distribution and damaged position detection method of water barrier layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain accurately a resistivity distribution of the ground or a reclaimed land. SOLUTION: This method for obtaining the resistivity distribution of the ground or the reclaimed land is characterized by comprising a preliminary measuring process for measuring a potential distribution of the ground or the reclaimed land and a calculation process for calculating the resistivity distribution of the ground or the reclaimed land based on the potential distribution measured in the preliminary measuring process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a specific resistance distribution on a ground or a landfill and a method for detecting a damaged position of a water impermeable layer of a water impermeable structure.

[0002]

2. Description of the Related Art A method of determining a specific resistance distribution of a ground or a landfill includes a method in which measurement electrodes are densely arranged and a direct measurement is performed by a four-electrode method or the like. Then, there is a method of obtaining the specific resistance around the measurement electrode. In addition, taking the impermeable layer of a landfill, which is a impermeable structure, as an example, the conventional method for detecting the damage position of the impermeable layer is a method for detecting the damage between the power supply electrodes installed between the electrically high-impedance impermeable layers. For example, a current is caused to flow between the inside and outside of the landfill, and the potential distribution generated above or below the impermeable layer or between the impermeable layers in the case of a double impermeable layer structure is measured. Then, the damaged position of the impermeable layer is detected from the potential strain generated around the damaged position.

[0003]

The above-mentioned conventional method for obtaining the resistivity distribution has the following problems. <a> In order to directly obtain the specific resistance distribution accurately, the measurement electrodes need to be densely arranged. For this reason, installation of the measuring electrode requires cost and time. <B> Since the error at the end of the range where the measurement electrodes are arranged increases, it is necessary to increase the electrode density particularly at the end. When applied to landfills, the measurement range becomes wider as the landfill progresses.To arrange the electrodes so that the electrodes at the ends are always dense, arrange the electrodes densely over a wide area. There is a need. <C> When the shape of the measurement range is complicated (such as a final disposal site), there is a problem that a measurement error increases.

[0004] The above-mentioned conventional method for detecting a damaged location of a water-impervious layer has the following problems. <B> When waste is landfilled in the landfill,
Potential distribution is affected by the non-uniformity of landfill waste and its distribution. As a result, the potential distortion generated around the damaged position is also affected, and the error may increase. <B> The above problems also occur due to differences in the position of the power supply electrode and the shape of the landfill. <C> In a landfill that is being reclaimed, the electrical conditions (eg, resistivity distribution) in the landfill change daily with the progress of the landfill, so if you solve with a fixed model, errors will increase with the progress of the landfill. However, there is a possibility that the damaged position of the impermeable layer cannot be detected accurately.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to accurately obtain a resistivity distribution of a ground or a landfill. Alternatively, it is another object of the present invention to accurately detect a damaged position of a water-blocking layer of a water-blocking structure using a specific resistance distribution obtained with high accuracy. Alternatively, damage to the impermeable layer accurately without being affected by background potential distribution such as unevenness of conductivity inside and outside, influence of electric potential distribution by the position of the feeding electrode, influence of electric potential distribution by the shape of the impermeable structure The purpose is to detect the position. Or
In the case of a landfill that is being reclaimed, the electrical conditions in the landfill change daily as the reclamation progresses. It is an object of the present invention to accurately detect a damaged position of a water barrier layer without being affected by a potential distribution due to this. The present invention achieves at least one of these objects.

[0006]

In order to achieve the above object, a method of determining a resistivity distribution according to the present invention is a method of determining a resistivity distribution of a ground or a landfill, comprising the steps of: The method is characterized by comprising a preliminary measurement step of measuring the distribution and a calculation step of calculating a resistivity distribution of the ground or the landfill based on the potential distribution measured in the preliminary measurement step. Here, the calculation step assumes an initial value of the resistivity distribution of the ground or landfill, and a potential distribution calculated by giving the current of the ground or the landfill at the time of the preliminary measurement step to the resistivity distribution, Compare with the potential distribution measured in the preliminary measurement step,
By changing the initial value of the specific resistance distribution based on the comparison result, it is possible to calculate the specific resistance distribution such that the calculated potential distribution becomes substantially the same as the potential distribution measured in the preliminary measurement step. In the preliminary measurement step, a power supply electrode may be installed at at least two places on the ground or in a landfill, and a current may flow between the power supply electrodes to measure a potential distribution. Further, in the method for detecting a damaged position of a water impervious layer according to the present invention, in the method for detecting a damaged position of a water impervious layer having high electrical resistance, a power supply electrode is provided at at least two places on one side of the water impervious layer. Then, the specific resistance distribution in the vicinity of the impermeable layer is obtained by the method for obtaining a specific resistance distribution of the present invention, and the potential distribution in the vicinity of the impermeable layer is calculated from the specific resistance distribution, assuming that a current flows between the impermeable layers. Analysis step, and the main measurement step regardless of the order of the analysis step,
A difference potential distribution is obtained from the difference between the main measurement step of measuring the potential distribution generated near the water impervious layer by flowing a current between the water impervious layers, the potential distribution calculated in the analysis step, and the potential distribution measured in the main measurement step. It comprises a comparison step to be created and an estimation step to estimate the presence or absence of damage and its position from the difference potential distribution. Here, when the water impermeable layer has a double structure composed of two layers, it is also possible to detect at least one damaged position of the water impermeable layer.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for obtaining a resistivity distribution according to the present invention will be described below with reference to FIG.

<A> Preliminary measurement step The preliminary measurement step is a step of measuring the potential distribution on the ground or landfill. The potential distribution is measured, for example, with a potential measuring electrode 4 installed at a predetermined interval on the ground or a landfill. The potential measuring electrodes 4 are, for example, in the form of a grid at equal intervals in the vertical and horizontal directions, and are arranged in a plurality of stages at intervals in the depth direction. Here, it is necessary to grasp the current of the ground or landfill at the time of measuring the potential distribution. For this purpose, for example, a known current is passed between the power supply electrodes 2, and the potential distribution is measured by the potential measurement electrode 4. Further, natural current or the like existing in the ground or landfill may be used. The potential distribution is measured by, for example, passing a current between the power supply electrodes 2 and
This is performed by measuring as a potential difference between the potential measurement electrode 4 and the reference electrode 8. As a current flowing between the power supply electrodes 2, for example, an alternating current, an alternating current, or the like is used.

<B> Calculation Step The calculation step is a step of calculating the distribution of the specific resistance of the ground or landfill (hereinafter referred to as the specific resistance distribution) based on the potential distribution at the time of the preliminary measurement step. First, an analysis model having the same shape as the ground 70 is created. Then, an initial value of the specific resistance distribution is given on the analysis model. Next, in the analysis model given the initial value of the resistivity distribution,
For example, the potential distribution of the ground 70 is calculated on the assumption that a current has flowed between the power supply electrodes. The calculated potential distribution is compared with the potential distribution measured in the preliminary measurement step, and the initial value of the specific resistance of the portion where the potential distribution is different is corrected. Then, a resistivity distribution is calculated such that the calculated potential distribution becomes substantially the same as the potential distribution in the preliminary measurement step.

An embodiment of a method for detecting a damaged position of a water barrier layer according to the present invention will be described below with reference to the drawings.

<A> Installation of Feeding Electrode and Potential Measurement Electrode Hereinafter, description will be made with reference to FIG. The impermeable structure is a landfill for general or industrial waste,
What is necessary is just to have a water-blocking structure, such as a reservoir, and a landfill is taken as an example in the embodiment. The ground at the landfill site is excavated, and a water-resistant impermeable layer 1 is laid on the bottom and side surfaces thereof. For example, a rubber sheet or the like is used for the water blocking layer. Potential measurement electrodes 4 are provided at predetermined intervals in the vicinity of the impermeable layer 1. Here, the vicinity of the impermeable layer only needs to be near the impermeable layer 1 and may be in contact with the impermeable layer 1. For example, they are arranged in a grid at equal intervals in the vertical and horizontal directions. At least two internal power supply electrodes (21, 22) are installed on the side of the impermeable layer 1 where the potential measurement electrodes 4 are installed. Then, for example, an external power supply electrode 31 is provided outside the landfill 7. Further, it is desirable to install an internal reference electrode 20 and an external reference electrode 30 inside and outside the landfill 7, respectively. In FIG. 2, the potential measurement electrode 4 is provided on the upper surface of the impermeable layer 1, but may be installed on the lower surface of the impermeable layer 1.

<B> Specific resistance distribution A specific resistance distribution near the impermeable layer is obtained. For example, first, a current is applied to one side of the impermeable layer 1 as a boundary, and a potential distribution generated near the impermeable layer 1 is measured. The potential distribution is measured, for example, by using the internal power supply electrodes (21, 22).
Is conducted by measuring a potential distribution generated in the vicinity of the impermeable layer 1 as a potential difference between the potential measuring electrode 4 and the internal reference electrode 20. Here, the external reference electrode 30 may be used in place of the internal reference electrode 20, or the potential distribution may be measured as the potential difference between the potential measurement electrodes without using the reference electrode. As a current flowing between the internal power supply electrodes (21, 22),
For example, an alternating current, an alternating current, or the like, whose polarity alternates, is used. When power is supplied between the power supply electrodes (for example, between the internal power supply electrodes) provided only on one side of the water impermeable layer, the potential distribution can be obtained without being affected by the presence or absence of damage to the water impermeable layer. This is because the current passing through the damaged portion is much smaller than the current flowing in the landfill 7.

The specific resistance distribution near the impermeable layer is determined so as to match the potential distribution measured by the above method. The method of calculating the resistivity distribution assumes that, for example, a landfill having the same shape as the landfill 7 (hereinafter referred to as an analysis model) is used, and that a current flows between the internal power supply electrodes in the same manner as the above-described potential distribution is measured. Then, a specific resistance distribution is obtained so as to show a potential distribution substantially the same as the measured potential distribution.

<C> Analysis Step The analysis step is a step of calculating the potential distribution in the vicinity of the impermeable layer 1 using the analysis model having the specific resistance distribution calculated as described above. For example, assuming that a current has flowed between the internal power supply electrode 21 and the external power supply electrode 31 as shown in FIG. 3 on the analysis model, the potential distribution generated by the specific resistance distribution near the impermeable layer is calculated.

<D> Main Measurement Step The main measurement step is a step of passing a current between the water-blocking layers 1 and measuring the potential distribution generated near the water-blocking layer 1. For example, as shown in FIG. 3, power is supplied between the internal power supply electrode 21 (or 22) and the external power supply electrode 31, and the potential distribution is measured by the potential measurement electrode 4. FIG. 4 shows an example of an equipotential diagram of the measured potential distribution in the main measurement step.

<E> Estimation of Damage Position The damage position is estimated using the potential distribution calculated in the above analysis step and the potential distribution measured in the main measurement step. The order of the analysis step and the main measurement step may be either first or simultaneous. The difference between the potential distribution in the analysis step and the potential distribution in the main measurement step is referred to as a differential potential distribution. FIG. 5 shows an example of an equipotential diagram of the differential potential distribution. Here, a position where equipotential lines of the differential potential distribution are densely illustrated is estimated as a damaged position. For example, an equipotential diagram of the differential potential distribution is created, and if there is a concave (or convex) portion, the lowest position (or the highest position) of the concave is estimated as the damaged position.

[0017]

Embodiment 1

<A> Measurement of electric potential distribution The electric potential distribution is measured, for example, at 5 to 30 m on the ground or landfill.
With the potential measuring electrodes 4 arranged in a grid at a pitch of. For example, a state in which no current flows for a certain period of time at a certain interval appears between the power supply electrodes, and an alternating current having a waveform whose polarity is changed flows.

<B> Calculation of resistivity distribution First, an analysis model having the same shape as the ground 70 or the landfill 7 is created. Then, an initial value of the specific resistance distribution is given to, for example, the inside of the landfill near the water-blocking layer 1 on the analysis model. Next, in the analysis model given the initial value of the resistivity distribution,
Assuming that a current has flowed between the power supply electrodes, the potential distribution near the impermeable layer is calculated. This result is defined as the potential based on the analysis result. The potential based on the analysis result is compared with the potential of the potential distribution at the time of the main measurement step, and the initial value of the specific resistance distribution is corrected by the following equation.

[0020]

(Equation 1)

The correction of the specific resistance is performed for a plurality of points on the ground or landfill. The process is repeated as necessary until the potential distribution in the analysis result matches the potential distribution in the main measurement step. The potential distribution in the vicinity of the impermeable layer, for example, is calculated by an analysis model in which the calculated specific resistance distribution is set.

<C> Estimation of Damage Position An electric current is applied between the impermeable layers 1 and the potential distribution generated near the impermeable layers 1 is measured. The potential distribution at the time of the analysis step is subtracted from the potential distribution at the time of the main measurement step to obtain a differential potential distribution. A position having the lowest potential on the differential potential distribution diagram with the internal power supply electrode set to + and the external power supply electrode set to-can be estimated as the damage center position. The following method can be used as a method for estimating the position with the lowest potential. As a first method, a mean square error between a theoretical value obtained by applying a theoretical expression indicating a potential change around the damage assuming the damage position and the difference potential distribution is obtained, and the damage position at which this error is minimized is calculated. Is available. Here, the theoretical formula is shown below.

[0023]

(Equation 2)

As a second method, it is possible to use a method of specifying the damage position from the coincidence between the potential distribution obtained from the numerical simulation analysis and the difference potential distribution.

[0025]

[Embodiment 2] An embodiment in which the water barrier layer has a double structure will be described below. <A> When the external power supply electrode is installed inside the impermeable layer FIG. 6 is a schematic diagram. In this case, the external power supply electrode 31 and the external reference electrode 30 are provided in a range surrounded by the upper water-impervious layer 11 and the lower water-impervious layer 12. This makes it possible to detect the position of the upper impermeable layer 11 when it is damaged. In addition, when the internal power supply electrode and the potential measurement electrode are installed below the lower impermeable layer 12, the damaged position of the lower impermeable layer 12 can be detected.

<B> When the power supply electrode and the potential measurement electrode are installed inside the water blocking layer. FIG. 7 is a schematic diagram. In this case, the feeding electrodes (3
3, 35) and reference electrodes (32, 34). In this case, the damage position of the upper impermeable layer 11 is also changed to the lower impermeable layer 1.
The two damaged locations can also be separately detected.

<C> Other Cases It is of course possible to form the water barrier layer shown in FIG. 2 into a double structure. By doing so, the upper impermeable layer 11 and the lower impermeable layer 1
When both of them are damaged, the damaged position of the upper impermeable layer 11 can be detected. In addition, the water impermeable layer shown in FIG.
1 can be installed inside the landfill, and the internal power supply electrodes (21, 22) and the potential measurement electrode 4 can be installed near the lower impermeable layer 12 outside the landfill. By doing so, the upper impermeable layer 11
When both the lower water-impervious layer 12 and the lower water-impervious layer 12 are damaged, the damaged position of the lower water-impervious layer 12 can be detected.

[0028]

As described above, the method for obtaining the resistivity distribution of the present invention has the following effects. <A> A specific resistance distribution is determined such that the measured potential distribution matches the calculated potential distribution. Therefore, the specific resistance distribution of the ground or the landfill can be obtained with high accuracy. <B> A specific resistance distribution can be obtained with high accuracy without increasing the number of measurement electrodes as compared with the conventional method. Therefore, it is not necessary to spend cost and time to install a measuring instrument for improving accuracy.

Further, since the method for detecting a damaged position of a water barrier layer of the present invention is as described above, the following effects can be obtained. <B> It is possible to accurately detect the damage position of the impermeable layer of the impermeable structure. <B> Before estimating the damage location, remove the effects of background potential distribution such as non-uniformity of conductivity inside and outside, the influence of potential distribution by the position of the feeding electrode, and the influence of potential distribution by the shape of the impermeable structure. . For this reason, the damaged position of the impermeable layer can be accurately detected. <C> The damaged position of the impermeable layer can be detected accurately without increasing the number of measurement electrodes as compared with the conventional method. Therefore, the construction cost of the landfill is not increased to improve the accuracy. <D> Even when applied to a landfill having a complicated shape, the damaged position of the impermeable layer can be accurately detected without increasing the number of measurement electrodes. <E> Even when the method is applied to a landfill that is being reclaimed, the damaged position of the impermeable layer can be accurately detected without being affected by changes in electrical characteristics accompanying the progress of the landfill.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a case of obtaining a specific resistance distribution according to the present invention.

FIG. 2 is a schematic diagram of a case where power is supplied between internal power supply electrodes according to the present invention.

FIG. 3 is a schematic diagram of a case where power is supplied between an internal power supply electrode and an external power supply electrode.

FIG. 4 is a display example of an equipotential diagram of a measured potential distribution.

FIG. 5 is a display example of an equipotential diagram of a differential potential distribution.

FIG. 6 is a schematic view of an embodiment in which the water impermeable layer has a double structure and an external power supply electrode is installed inside the water impermeable layer.

FIG. 7 is a schematic diagram of an embodiment in which a water impermeable layer has a double structure and a power supply electrode and a potential measurement electrode are installed inside the water impermeable layer.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Takashi Ono 1499-31, Omuro, Kashiwa City, Chiba Prefecture (72) Inventor Toshiro Oshigata 1-25-1, Nishishinjuku, Shinjuku-ku, Tokyo Taisei Corporation F term (reference) 2G067 AA01 AA19 BB11 CC02 DD23 EE08 4D004 AA46 BB06 DA01 DA20

Claims (5)

[Claims] 1. A method for determining the resistivity distribution of a ground or a landfill, comprising: a preliminary measurement step of measuring the potential distribution of the ground or the landfill; and a ratio of the ground or the landfill based on the potential distribution measured in the preliminary measurement step. A method for determining a resistivity distribution, comprising a calculating step of calculating a resistance distribution. 2. The method according to claim 1, wherein the calculating step assumes an initial value of the resistivity distribution of the ground or the landfill, and calculates a potential distribution calculated by giving the current of the ground or the landfill at the time of the preliminary measurement step to the resistivity distribution. And, the potential distribution measured in the preliminary measurement step, and compared, the initial value of the specific resistance distribution is changed based on the comparison result, the calculated potential distribution is substantially the same as the potential distribution measured in the preliminary measurement step 2. The method according to claim 1, wherein a specific resistance distribution is calculated. 3. The pre-measurement step is characterized in that power supply electrodes are installed at at least two places on the ground or in a landfill, and a current is passed between the power supply electrodes to measure a potential distribution. A method for obtaining the specific resistance distribution described. 4. A method for detecting a damage position of a water-impervious layer having high electrical resistance, comprising: providing a power supply electrode at at least two places on one side of the water-impervious layer; An analysis step of calculating a potential distribution in the vicinity of the impermeable layer from the specific resistance distribution, assuming that a current has flowed between the impermeable layers, and an analyzing step. In this measurement step, regardless of the order, this measurement step measures the potential distribution generated near the water impermeable layer by passing current between the water impermeable layers, the potential distribution calculated in the analysis step, and the measurement in the main measurement step A method for detecting a damaged position of a water-impervious layer, comprising: a comparing step of creating a differential potential distribution based on a difference from the obtained potential distribution; and an estimating step of estimating the presence or absence of damage and its position from the differential potential distribution. 5. The method according to claim 4, wherein the water-impervious layer has a double structure consisting of two layers.
A method for detecting a damaged position of a water impermeable layer, comprising detecting a damaged position of at least one layer of the water impermeable layer.