JPS6027388B2 - Method for measuring groundwater flow velocity, groundwater flow direction, and measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring flow velocity and flow direction of groundwater and its device, and its main purpose is to improve measurement accuracy and reliability.

In construction work, it is necessary to measure the flow velocity and direction of groundwater, including underground water, for each stratum.

For this purpose, physical logging is generally used, as well as tracer methods and various salts or pigments are used. In this case, in order to detect the tracer, it is necessary to bring the instrument into direct contact with the groundwater, or to sample the groundwater in undisturbed conditions, but this is generally difficult and uncertain and involves stratified conditions, and the current location of each stratum is difficult and uncertain. cannot be measured non-destructively. Furthermore, it becomes difficult to obtain accurate values due to tracer diffusion, mixing, adsorption, etc. Therefore, the present inventors proposed patent No. 827136 and
As shown in No. 306, we proposed a method (hereinafter referred to as the conventional method) of measuring the flow velocity and/or flow direction of groundwater from the diluted state in an observation hole in which a neutron moisture meter was installed. However, the conventional method has the following drawbacks.

In other words, {1- The diameter of the observation hole is large because measurements are taken from the diluted state inside the hole, and ■Each time the flow rate is measured, the instrument must be raised to the ground and the tracer must be set, making the measurement intermittent. {31) It is necessary to mix the tracer and groundwater uniformly, and if the mixing is not uniform, the measurement accuracy and reliability are poor; However, in the conventional method, the flow direction is determined by the dilution gradient of the tracer in each direction in the pipe, so it is necessary to carefully adjust the specific gravity to prevent density flow from occurring due to the difference in specific gravity between the tracer and groundwater. (2) It is difficult to use a tracer when the flow rate is high. The inventors of the present invention have conducted extensive research to solve these problems, and have discovered that it is sufficient to inject a tracer into the ground and measure the movement of the tracer, and have arrived at the present invention.

That is, the first invention installs a neutron moisture meter in the ground, feeds a tracer made of a nuclide with a large thermal neutron absorption cross section mainly to the height of the neutron moisture meter, and also adjusts the porosity of the ground in advance. A standard dilution of the tracer being considered is determined, the dilution of the currently injected tracer is measured by the neutron moisture meter, and the groundwater flow velocity is measured from the measured dilution and the standard dilution. This is a method for measuring groundwater flow velocity.

The second invention is to install a directional neutron moisture meter in the ground, feed a tracer made of a nuclide with a large thermal neutron absorption cross section mainly to the height of the neutron moisture meter, and This is a method for measuring the flow direction of groundwater, characterized by determining the rotation count rate around the axis or calculating the dilution of the tracer from this count rate, and measuring the flow direction of the groundwater from the count rate or dilution.

The third invention is installed in an insertion hole drilled in the ground, and includes a neutron moisture meter, a packer installed above and below the neutron moisture meter, and thermal neutrons from the ground to the ground around the neutron moisture meter. 1. A device for measuring flow velocity and/or flow direction of groundwater, characterized by comprising means for delivering a tracer made of a nuclide with a large absorption cross section.

The present invention will be explained below with reference to a concrete example. 1 is a neutron moisture meter with directivity, and an amplifier 2 is mounted on the top of the neutron moisture meter.
is provided, and its detection signal is sent to the ground via a signal cable 3.

A tube 4 is wrapped around the amplifier 2, forming a tracer flow path 5. Numerals 6 and 6' are flexible packers that cover the tube 4 in a cylindrical shape.

A tracer T, which will be described later, is fed from the ground to the tracer flow path 5 via a tracer pressure feed pipe 7, and is discharged from a lower discharge port 8 to the surrounding ground. Air supply pipes 9 and 9' are designed to inflate the packers 6 and 6' by feeding air under pressure from the ground.

It is a support rod.

Reference numeral 11 denotes a gripping rod, and by operating this rod 11, the entire meter can be moved up and down, or only the moisture meter 1 can be rotated around its axis.

During measurement, an observation hole is drilled in a predetermined measurement ground 12, and a filter pipe 13 having a large number of through holes formed in the surrounding wall is installed in the hole to prevent the observation hole from collapsing.

Next, after suspending the entire instrument to the observation position inside the filter pipe 13, the air pump 14 is activated and the air pump 6
, 6' are expanded to fix the entire meter inside the filter pipe 13. Then, the tracer T is pumped by the tracer injection pump 15 and discharged from the discharge port 8 to form the surrounding ground 12.
have it injected. On the other hand, when the groundwater flow is weak, a small amount of tracer T is sent into the neutron moisture meter 1 position in the filter pipe 13 via the tracer flow path 5 without forcibly injecting the tracer T, and then the packer
6, 6' may be inflated to fix the entire instrument.

In this way, groundwater W flows in through the through hole in the filter pipe 13 and flows away with the tracer T.
Flow velocity and flow direction can be measured using principles similar to those described below. Here, a nuclide with a large thermal neutron absorption cross section is used as the tracer.

For example, boron (?55 burn), cadmium (2550 burn)
Burn), mercury (0 burn), indium (190 burn), etc. are used. Especially in practical use, it is a water-soluble compound,
A suitable material is a boron compound, which is relatively easy to obtain and safe. Thus, as the groundwater W flows, the concentration of the tracer injected (delivered) into the ground or in the vicinity of the moisture meter 1 decreases.

The dilution state of the concentration is measured by the moisture meter 1 and the scaler 16, a shark normal curve as shown in FIG. 5 is obtained in advance, and the flow rate is determined from this standard dilution and the measured dilution. In order to obtain a shark normal curve, a shark normal curve corresponding to the porosity is required because the sulfur velocity varies depending on the porosity of the target ground even if the dilution gradient is the same.

In this respect, it is advantageous to use the neutron moisture meter 1 as in the above example because the porosity of the ground can be determined by the moisture meter 1 before tracer injection. To measure the groundwater flow velocity for each stratum, it is sufficient to move the entire device up and down. The same applies to the next flow direction. When measuring the flow direction, rotate the moisture meter 1 around the axis to find the direction of the maximum dilution of the tracer,
This determines the flow direction.

Measurement examples are shown in FIGS. 6 and 7. If the flow velocity is far, it is only necessary to continuously inject tracer T and know in which direction it flows away. In the above example, the packers 6, 6' are used to fix the device around the hole and to make the underground water flow parallel.

In addition, when measuring flow velocity, a moisture meter does not necessarily have to be directional, but in order to measure the flow direction, the minimum count rate and maximum dilution direction are required, so it is necessary to use a directional moisture meter. It needs to be something. Furthermore, filter pipe 1
3 is not necessarily necessary, but if this is used, the flow velocity must be measured due to the influence of the filter pipe. As described above, the present invention uses a nuclide with a large thermal neutral absorption cross section instead of using an isotope solution as a tracer, so it is safe to handle.
In particular, since the tracer is mainly injected into the ground and the flow velocity and/or flow direction is determined from the state of dilution with groundwater, it differs from the secondary method, which determines the state of dilution inside the observation hole, because the observation hole is small. It is possible to make repeated measurements at the same location without having to raise the instrument to the ground each time, there is no inconvenience that accuracy cannot be guaranteed unless the tracer and groundwater are mixed uniformly, and there is no inconvenience when measuring flow direction. Since the groundwater and tracer flowing through the ground gap are measured, density flow is not a problem and the measurement accuracy is good, and the flow direction can be measured even when the flow velocity is high.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the arrangement of the measuring device, Fig. 2 is a front view of the device, Fig. 3 is a longitudinal sectional view of the main part, Fig. 4 is a view taken along the line A-A, and Fig. 5 is a shark normal curve. FIG. 6 and FIG. 7 are diagrams showing examples of flow direction measurement. 1...Neutron moisture meter, 2...Amplifier, 3.
...Signal cable, 4...Tube, 5...Tracer flow path, 6,6'...Pass car, 7...
Tracer pressure feed pipe, 8...Discharge port, 9,9'...
・Air supply pipe, 10...Support rod, 11
...Gripping rod, 12...Ground, 13
... Filter pipe, 14 ... Air pump, 15 ... Tracer injection pump, 16
...Scaler. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Scope of Claims] 1 A neutron moisture meter is installed in the ground, and a tracer consisting of a nuclide with a large thermal neutron absorption cross section is placed mainly at the height of the neutron moisture meter.A tracer standard that takes into account the porosity of the ground in advance. A method for measuring the flow velocity of groundwater, characterized in that the degree of dilution is determined, the degree of dilution of the tracer injected at the moment is measured by the neutron moisture meter, and the flow rate of groundwater is measured from the measured dilution degree and the reference dilution degree. Measuring method. 2. The method for measuring the flow velocity of groundwater according to claim 1, wherein packers are provided above and below the neutron moisture meter, and the tracers are injected mainly into the ground at the height of the neutron moisture meter. 3 A directional neutron moisture meter is installed in the ground, a tracer consisting of a nuclide with a large thermal neutron absorption cross section is delivered mainly to the height of the neutron moisture meter, and the neutron moisture meter is rotated around its axis. 1. A method for measuring the flow velocity of groundwater, which comprises: obtaining a count rate or calculating a degree of dilution of a tracer from this count rate, and measuring the flow direction of groundwater from the count rate or degree of dilution. 4. A method for measuring the flow velocity of groundwater according to claim 3, wherein packers are provided above and below the neutron moisture meter, and these packers inject the tracer mainly into the ground at the height of the neutron moisture meter. . 5. A neutron moisture meter installed in an insertion hole drilled in the ground, a neutron moisture meter, a packer installed above and below it, and a nuclide with a large thermal neutron absorption cross section that is transported from the ground to the ground around the neutron moisture meter. A device for measuring the flow velocity and/or flow direction of underground water, characterized in that it is equipped with a means for sending a tracer consisting of: 6. The device for measuring the flow velocity and/or flow direction of groundwater according to claim 5, wherein the neutron moisture meter is a directional neutron moisture meter, and the neutron moisture meter is rotatable around an axis from the ground.