JPH08240550A - Ground water penetration property measuring method and device - Google Patents

Abstract

PURPOSE: To limitedly perform grouting operation by accurately obtaining the depth of a part with a high ground water penetration property utilizing the shifting phenomenon of water. CONSTITUTION: First and second electrodes 13 and 14 are inserted into first and second drilling holes 11 and 12 formed on a ground 10 to enable the first and second electrodes to face each other via the ground. An oscillation voltage is applied between the first and second electrodes by an oscillation circuit 15 and a conduction current between the first and second electrodes is detected by a current detection circuit 17. Further, by referring to the frequency of the oscillation voltage by a phase detection circuit 18, the waveform of the conduction current is detected to generate a waveform signal. The frequency component of the oscillation voltage is removed from the waveform signal by a filter circuit 19 to make remaining frequency components as modulation components.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the water permeability of the ground.

[0002]

2. Description of the Related Art When constructing a dam, the presence or absence of water leakage through the foundation ground is an important factor. It is expected that the shatter zone will be a water area as well as the degraded area of the foundation ground. For this reason, particular attention is paid to the existence of shatter zones in the basic ground survey of dams. Concretely, surface geological survey, boring survey, lateral hole survey, elastic wave survey, impedance survey between boreholes, etc. are conducted. When water passes through the crush zone, it reacts with the rock fragments that have been crushed and the surface area has increased, and a water absorption reaction occurs, changing from feldspars and mica to clay substances. Some clay substances, such as montmorillonite, expand in volume when they contain water, and the existence of ground permeability is an important factor.

For these reasons, ground boring is performed to investigate the water permeability of the ground, core samples are obtained, and this is investigated. When cracks are found in the core sample, cement milk is injected from the boring hole to perform grouting work to close the cracks in the ground. As a means for determining the effect of the grouting work, the elastic wave velocities of the ground before and after the grouting work are measured and compared. When the grouting work effectively works, the ratio of the low-speed component of the elastic wave propagation velocity around 2400 m / s is remarkably reduced as compared with that before the grouting work, so that the effect of the grouting work is judged.

The Lugeon test is also conducted as a means for judging the strength of the ground. The Lugeon test is a test in which high-pressure water is injected into a boring hole and the water permeability of the ground is evaluated based on the water permeability. Therefore, the Lugeon test has advantages that it can be carried out relatively easily and the ground condition can be roughly judged.

[0005]

However, the method of judging the presence or absence of water flow from the core sample cannot be judged when the collected core sample is not actually obtained from the place where the water flow exists. In addition, because the method using elastic wave survey and Lugeon test cannot accurately determine the depth at which the ground water channels exist, grouting work must be performed more than the required number of times to generate unnecessary cracks in the ground and It has the drawback of making a road. Further, the Lugeon test has a problem that the effect of the injection cannot be judged until the injection is actually performed because the injection pressure management and the histogram creation are necessary for the judgment.

Further, in the method of judging the presence or absence of a water channel by the impedance survey, a measurement error occurs when the specific resistance of the ground changes due to grouting work or when an aquifer exists in the ground. It is necessary to measure the depth of the actual water flow in the ground.

Therefore, an object of the present invention is to accurately determine the depth of a portion of the ground where water permeability is high by utilizing the movement phenomenon of water, thereby making it possible to limit the grouting work. It is to provide a measuring method and an apparatus.

[0008]

According to the present invention, the first and second electrodes are opposed to each other via the first portion of the ground, and an oscillating voltage is applied between the first and second electrodes. Then, the modulation component of the energizing current that has been applied between the first and second electrodes is detected by referring to the oscillation voltage, and the first and second electrodes are inserted through the second portion of the ground. Oscillating voltage is applied between the first and second electrodes facing each other, and the modulation component of the energizing current passed between the first and second electrodes is detected by referring to the oscillating voltage. A ground water permeability measuring method characterized by including the above is obtained.

Further, according to the present invention, the first and second electrodes are arranged so as to face each other across the ground, and an oscillation circuit for applying an oscillation voltage between the first and second electrodes, A current detecting circuit for detecting a current flowing through the first and second electrodes; and a modulation component detecting means for detecting a modulation component of the current by referring to the oscillation voltage. A ground water permeability measuring device is obtained.

[0010]

When a water channel exists in the ground between the first and second electrodes, the electric conductivity of the water channel portion is higher than that of the other portions, so that the energizing current tends to increase. Furthermore, the electric conductivity of the water channel changes dynamically due to the influence of the water flowing through the water channel. In particular, since water also contains fine particles, the resistance between the first and second electrodes slightly changes with the flow of water, and the electric conduction is dynamically changed. Due to this change in electrical conductivity, the energized current undergoes amplitude modulation at a frequency different from the frequency of the oscillating voltage and has a modulation component. Therefore, by measuring the modulation component contained in the energizing current, the depth of the location of the water channel in the ground can be accurately obtained. For this reason, the place where the grouting work is required is limited, and the waterproof effect by the grouting work can be determined by performing the same measurement after the grouting work.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an overall configuration of a ground water permeability measuring apparatus according to an embodiment of the present invention. This ground water permeability measuring device is a device suitable for measuring the water permeability of the ground 1 when constructing a dam or the like. Prior to the measurement of water permeability, first and second boring holes 11 and 12 are provided in the ground 10. The first boring hole 11 has a second electrode 13
The second electrodes 14 are arranged in the respective boring holes 12. Thus, the first and second electrodes 13 and 14 are arranged so as to face each other with the ground interposed.

An oscillating circuit 15 is connected between the first and second electrodes 13 and 14 to apply an oscillating voltage of a predetermined frequency, for example, about 1 KHz. As a result, when the water-permeable layer 16 exists in the ground 10, the first and second electrodes 1
A current flows between 3 and 14 as an energizing current. A current detection circuit 17 is connected between the oscillation circuit 15 and the second electrode 14 in order to detect this energized current.

The ground water permeability measuring apparatus further includes a phase detection circuit 18 and a filter circuit 19. The phase detection circuit 18 is connected to the oscillation circuit 15 and the current detection circuit 17, and detects the waveform of the energizing current described above at the frequency of the oscillation voltage and generates a waveform signal. Filter circuit 19
Is connected to the oscillating circuit 15 and the current detecting circuit 17, and removes the frequency component of the oscillation voltage of the oscillating circuit 15 from the above-mentioned waveform signal and uses the remaining frequency component as the modulation component. Specifically, the filter circuit 19 is a low-pass filter, and passes only the frequency component having a frequency lower than the above-mentioned predetermined frequency in the waveform signal. Phase detection circuit 1
8 and the filter circuit 19 together constitute a modulation component detecting means for detecting the modulation component of the energized current. The filter circuit 19 outputs the modulation component as an AC signal.

The ground water permeability measuring apparatus further includes a linear detection circuit 21 for linearly detecting the AC signal output from the filter circuit 19 to generate a DC signal.

In the measurement, the first and second electrodes 1
3, 14 are successively lowered into the first and second boring holes 11, 12. A phenomenon in which the energization current increases at a portion where water and fine particles such as bubbles flow in the crack of the ground 10. This phenomenon indicates that a crack exists in the ground 10.

Further, the energized current may have a low frequency component different from the above-mentioned predetermined frequency. This low-frequency component occurs when the size of cracks is equal to the size of minute particles such as bubbles, and causes a slight fluctuation in the energizing current. Therefore 1
By measuring the low-frequency component of KHz or less, not only the presence of cracks is detected, but also the presence of running water flowing through the cracks is measured due to current fluctuations due to resistance fluctuations in the cracks.

FIG. 2 shows an example of the relationship between the depth of the first and second electrodes 13 and 14 in the ground 10 and the applied current. Figure 2
As can be seen from the above, the first and second electrodes 13,
A phenomenon occurs in which the energizing current increases when 14 are opposed to each other.

FIG. 3 shows an example of the output of the linear detection circuit 21. As can be seen from FIG. 3, when the first and second electrodes 13 and 14 face the portion of the ground 10 where the electrical conductivity is high due to cracks, the component of different frequency rises in the variation component of the energizing current. Phenomenon occurs.

[0019]

As described above, according to the present invention,
The effect of injection is determined by comparing the measurement results before and after controlling the amount of cement milk injected by limiting the grouting work by detecting the locations of water channels that cause water leakage in the ground by on-site measurement. Can be determined. Therefore, the cement milk injection work can be carried out systematically, and the obtained economic effect is great. In addition, it is possible to prevent the ground from being damaged by performing unnecessary grouting work.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a ground water permeability measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of the relationship between electrode depth and energization current.

FIG. 3 is a graph showing an example of the output of a linear detection circuit included in the ground water permeability measuring apparatus of FIG.

[Explanation of symbols]

 10 Ground 11 First Boring Hole 12 Second Boring Hole 13 First Electrode 14 Second Electrode 15 Oscillation Circuit 16 Water-permeable Layer 17 Current Detection Circuit 18 Phase Detection Circuit 19 Filter Circuit 21 Linear Detection Circuit

Claims (4)

[Claims] 1. A first electrode and a second electrode are opposed to each other via a first portion of the ground to apply an oscillating voltage between the first electrode and the second electrode, and the first electrode and the second electrode. Detecting a modulation component of the energizing current that has been applied between them by referring to the oscillating voltage, and making the first and second electrodes face each other via the second portion of the ground to make them the first and second Applying an oscillating voltage between the electrodes, and detecting the modulation component of the energizing current applied between the first and second electrodes with reference to the oscillating voltage. Method. 2. A first electrode and a second electrode which are arranged so as to face each other via the ground, an oscillation circuit which applies an oscillation voltage between the first electrode and the second electrode, and the first and second electrodes. Two
A ground water permeability measuring apparatus, comprising: a current detection circuit for detecting an energized current that has been energized between the electrodes, and a modulation component detection means for detecting a modulation component of the energized current with reference to the oscillation voltage. 3. The phase detection circuit, wherein the modulation component detection means refers to the frequency of the oscillation voltage to detect the waveform of the energizing current to generate a waveform signal, and the frequency component of the oscillation voltage from the waveform signal. 3. The ground water permeability measuring apparatus according to claim 2, further comprising a filter circuit that removes the residual frequency component and uses the remaining frequency component as the modulation component. 4. The ground permeable water according to claim 3, wherein the filter circuit outputs the modulation component as an AC signal, and further includes a linear detection circuit that linearly detects the AC signal to generate a DC signal. Sex measuring device.