JPS6126884A - Movement surveying method of ground water - Google Patents

Abstract

PURPOSE:To survey the movement of ground water precisely by digging a boring hole of small bore diameter and measuring the three dimensional flow directional flow velocity of water in each water level in ground water in the hole. CONSTITUTION:Existence of permeated water 1 and existence of an impermeable layer 2 are ascertained by a survey of the ground surface and the surface level 5 of ground water is ascertained by an observation well 4. Boring holes 6a, 6b,-of small bore diameter are digged at the position required. A sensor is inserted into the hole to measure the three dimensional flow directional flow velocity of water in each water level of the ground water surface 5. The sensor consists of >=3 pieces ultrasonic wave oscillating elements 11, a ultrasonic receiving element 12 at the central part and a measuring part 13 incorporated with a direction detector. Measured data are transmitted to the ground by a communication cable incorporated in a flexible cable 14 and calculated by an analyzer to grasp the perfect movement of ground water at a measuring area from the result about the plural boring holes.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for investigating the dynamics of groundwater, and more specifically, the present invention relates to a method for investigating the dynamics of groundwater. Concerning how to precisely investigate.

[Conventional technology]

Groundwater dynamics research is an essential requirement for the use of water resources, the elucidation of permeability, landslides, and other geological strata, the design of structures and disaster prevention facilities, the construction planning of civil engineering works, and so on, so it has traditionally been conducted prior to these plans. An investigation was being conducted.

Conventional groundwater dynamics investigation methods include the two-dimensional current meter method, which measures changes in resistance between electrodes due to the movement of electrolyte, the isotope tracer method, the ordinary tracer method, and the propeller method.

In the two-dimensional current meter method, a large number of electrode rods are inserted into a container filled with a liquid with a specific electrical resistance different from that of water. The state in which the liquid is being replaced is detected from the change in resistivity between each electrode. Such an investigation method has the disadvantage that it requires drilling a large bore hole with a diameter of 100 mm or more.

The isotope tracer method uses radioactive isotopes and
Normally, the tracer method uses substances that are foreign to wood, such as electrolytes and dyes, and injects them into the injection hole, and observes their appearance in a separately dug observation hole. It is an essential requirement to drill observation boreholes, and only -dimensional or two-dimensional measurements can be performed. This method estimates three-dimensional groundwater movement from the groundwater table gradient or ground surface gradient.

This method not only increases survey costs because it requires drilling a large number of boreholes, but also involves estimation as described above.
Accuracy is not high.

The propeller method is a method in which a propeller driven by water flow is inserted into a borehole. Although it is possible to measure water flow in boreholes with relatively small diameters, it is limited to measuring only the component in one direction, for example, the vertical direction, and is not suitable for highly accurate surveys.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method for investigating the dynamics of groundwater, which improves the drawbacks of the above-mentioned conventional methods.

According to the present invention, it is not necessary to drill a large-diameter borehole, and the conventional amount of 6 6 m is easily carried out.
It is possible to measure the three-dimensional direction and flow velocity of water in the borehole using a borehole of mφ and without requiring separate injection holes and observation holes. Through this method, a high-performance, high-precision groundwater dynamics investigation method can be realized.

[Means for solving problems]

In order to achieve the above object, the present invention drills a small-diameter borehole, measures the three-dimensional flow direction and velocity of water at each water level in the groundwater in the borehole, and analyzes the dynamics of groundwater from the measured values. The gist of this paper is a groundwater dynamics investigation method that is characterized by:

Hereinafter, the method of the present invention will be explained in detail with reference to the drawings. FIG. 1 conceptually shows a method for investigating groundwater on a slope, schematically illustrating the method of the present invention.

When investigating water resources in the target area shown in FIG. 1, for example, the presence of seepage water 1 and the presence of an impermeable layer 2 are confirmed by a ground surface survey, and the groundwater level 5 is confirmed by observation and a well 4.

In the present invention, after conducting a ground survey of the actual condition of the target area to be investigated as described above, small-diameter boreholes 6a,
Dig 6b, 6c,...

The number of boreholes is determined depending on the actual situation of the object to be investigated and the purpose of the investigation, but in the method of the present invention, it is sufficient to drill a smaller number of boreholes than in any of the conventional methods. This is because three-dimensional flow direction and current velocity can be measured. The borehole is usually a vertical borehole, but it is also possible to use an inclined borehole depending on the actual situation.

The diameter of the borehole is 66, which is the most commonly used small diameter borehole.
mmφ is sufficient. Depending on the diameter of the borehole,
Since the machines used are also specialized, and the required costs vary greatly, the present invention has extremely excellent advantages in this respect both economically and technically.

Next, a sensor is inserted into the borehole to measure the three-dimensional flow direction and velocity of water at each water level of the groundwater table 5.

For this measurement, it is most suitable to use a sensor that utilizes ultrasonic waves developed by the present inventor.

Figure 2 shows the external appearance of such a sensor. The ultrasonic transmitting elements 11 face each other and are arranged at both ends of the same diameter on the circumference of a circle having a diameter of approximately 50 mmφ. The number is three or more. One receiving element 12 is installed at the center separated from the transmitting element 11 by a certain distance. The ultrasonic transmitting/receiving elements 11 and 12 are coupled to a measuring section 13 that includes an ultrasonic generating device and a receiving device.
is suspended in the borehole by a flexible cable 14.

The measuring part 13 has an outer diameter 6 to 10 mm larger than the diameter of the borehole.
It is relatively small, has a diameter larger than the diameter of the arrangement circle of the ultrasonic transmitting elements 11, has a length of about several tens of centimeters, is easily movable up and down along the borehole, and is ultrasonic. To guide a sound wave transmitting element 11 so as not to collide with the wall of a borehole. In addition, the ultrasonic transmitter/receiver element 1
A space is provided between 1° 12 and the measurement part 13 so as not to impede the three-dimensional direction and flow velocity of water.

Furthermore, a small azimuth detection device, for example, a compass using a small magnet and a Hall element, is built into the measurement unit 13.

The flexible cable 14 has sufficient strength to suspend the measurement unit 13 and flexibility to allow the measurement unit 13 to freely rotate within the port 1 non-hole, and connects the power line and the communication line. built-in). This cable 14 is wound around a suitable Cape Fred drum on the ground and held in a borehole so that it can be freely lowered and raised, thereby making it possible to detect the depth position of the ultrasonic transmitter/receiver in the borehole.

The ultrasonic waves sequentially time-divisionally transmitted from each element of the ultrasonic transmitting element 11 are sequentially received by the ultrasonic receiving element 12, and the difference in arrival time is measured on the order of IQ-12 seconds.

Now, if ΔT is the time difference L' between the pair of ultrasonic transmitting and receiving elements: the distance between the ultrasonic transmitting and receiving elements C is the speed of sound■ the flow velocity of water between the two ultrasonic transmitting and receiving elements, then ΔT=2VL/C2. There is a relationship, and by measuring ΔT, the flow velocity can be determined. In this case, changes in the sound speed C due to water temperature, density, etc. are automatically corrected by direct sound speed measurement between the transmitting and receiving elements. Using this method, by setting the spacing between the transmitting and receiving elements to be approximately several centimeters, the distance of 5 m
Flow velocities of approximately m 2 /sec or higher can be detected with high accuracy.

By measuring the distance between the above pair of transmitting and receiving elements for multiple transmitting elements, and analyzing the combination of these measurements and the positions of the transmitting and receiving elements, we can determine the three-dimensional flow direction and velocity of water in the borehole. is easily possible to measure.

This measurement analysis calculation can be performed immediately from data input to the ground analyzer via a communication cable built into the flexible cable 14. The output of this calculator can be recorded on a chart recorder, or can be input into a digital data logger, and can be connected to a computer to perform various analyses.

As described above, it is possible to measure upward flow, downward flow, and horizontal flow even within a single hole, and it is possible to obtain a three-dimensional flow velocity vector. Furthermore, the flow velocity vectors at each water level are measured in multiple boreholes, and the complete groundwater dynamics in the measurement area can be understood from these results.

For example, in Figure 1, there is an unconfined aquifer 7 above the impermeable layer 2, and its dynamics can be analyzed, the piezometer head surface 9 can be confirmed, and data for rational development of water resources in this area can be obtained. I can do it.

According to the method of the present invention, groundwater dynamics can be analyzed with extremely high accuracy, and surveys that meet advanced survey objectives can be easily provided in a short period of time and at low cost.

〔Example〕

The infiltration flow of river embankments was analyzed using the method of the present invention. There are several phenomena on river embankments that threaten the safety of the embankment due to flooding, one of which is a phenomenon called piping. This piping is a phenomenon in which when the seepage flow in the levee body exceeds a certain flow velocity (limit flow velocity) depending on the soil quality, the material of the levee body is washed away, leading to the destruction of the levee.

As shown in FIG. 3, boring holes 6a, 6b, . We analyzed the dynamics of

As a result, it is possible to compare the three-dimensional flow direction and flow velocity within the embankment body during floods and the critical flow velocity, and the danger of piping can be accurately determined, and measures can be taken to completely ensure safety during floods. was able to clarify.

In addition, we modeled the levee during a flood, performed seepage flow calculations using the finite element method, determined the flow velocity vector at the tip of the levee body where the flow velocity is maximum, and determined the relationship between the hydraulic conductivity of the levee body and the flow direction and velocity. However, it was possible to see a relatively good agreement between the calculated flow direction and flow velocity and the above-mentioned actually measured flow direction and flow velocity.

〔Effect of the invention〕

The present invention has a method of determining and analyzing the three-dimensional direction and flow velocity of water in a small-diameter borehole, making it possible to investigate the dynamics of groundwater at low cost and with high precision, making a major contribution.

[Brief explanation of the drawing]

FIGS. 1 and 3 are explanatory diagrams of the method of the present invention, and FIG. 2 is a perspective view of a sensor that can be suitably used in carrying out the method of the present invention.

Claims (1)

[Claims] 1. A groundwater dynamics investigation characterized by drilling a small-diameter borehole, measuring the three-dimensional flow direction and velocity of water at each water level in the groundwater in the borehole, and analyzing the dynamics of groundwater from the measured values. Method.