JPH06264431A - Water permeability tester - Google Patents

Abstract

PURPOSE:To obtain a water permeability tester by which an precise Water- permeation test can be carried out even in the ground having a low critical pressure and even in a deep zone and further, which has a wide range of the test pressure and a simplified, miniaturized and automatically processed measuring system. CONSTITUTION:This tester is provided with a packer 16 setting a water- permeation test zone A in the boring hole 12 formed in the ground 10 and a pressure sensor 20 equipped in the test zone. Water is forced to conduct from the pressurized water source on the ground (combination of a pump 22 and a pulsation-preventive tank 24, and a static pressure water tank 26) to the test zone through a water way. Water flow meters 30a, 30b and water flow rate adjusting valves 32a, 32b are equipped in the water way. The detected flow rate is compared with the preset flow rate and regulated by a flow rate adjuster 34 so that both figures coincide with each other. The flow rate and the pressure are recorded in a flow rate and pressure recorder 36.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for conducting a water permeability test using a boring hole. More specifically, it is a flow rate control system for maintaining a constant water injection amount per unit time, The present invention relates to a water permeation test device capable of measuring a water permeation pressure and a water permeation amount with high accuracy, speedily and automatically. This device is particularly useful for low hydraulic permeability tests in geologically distributed areas with low critical pressures.

[0002]

2. Description of the Related Art In dam construction surveys, it is important to accurately grasp the Lugeon value of the ground and the depth distribution of groundwater pressure in order to determine the construction position and grouting range. Also, in tunnel construction, it is necessary to understand the spring pressure and permeability near the tunnel formation in order to know the spring conditions during excavation. For these purposes, a water permeability test has been conventionally performed.

In the water permeability test, a water permeability test section is set by a packer in a boring hole formed in the ground, water is sent from the ground surface to the water permeability test section using a pump, and the pressure in the water permeability test section is measured by a pressure sensor. To do. According to the conventional method, water injection is continued until the planned pressure is reached, and after the planned pressure is reached, the flow rate is adjusted by operating the manual valve on the ground surface to keep the pressure constant, and the flow rate is adjusted every 1 minute. It was read by a meter and recorded. That is, the conventional technique is a pressure control system.

However, in this method, as the test depth increases (for example, a depth of 100 to 150 m), it becomes very difficult to control the permeation pressure, and especially in an area where the critical pressure is small, the pressure due to the excessively injected water pressure causes The ground was often destroyed during the conditioning phase. The reason is that when the permeability test section becomes deep, even if the water pressure by the pump is small, the head pressure from the ground surface to the groundwater level acts on the permeability test section, and if it is above the limit pressure of the ground, the ground is destroyed. This is because the true hydraulic conductivity of the ground cannot be obtained. Moreover, even if the head pressure is below the pressure limit of the ground, since a large head pressure is already applied, it is necessary to control the water injection pressure from the ground surface with an extremely small value, and further, the manual valve on the ground surface Since there is a large time lag until the effect of the operation appears as the indicated value of the pressure sensor in the water permeability test section, it is not easy for even a skilled person to predict the valve and operate the valve. Therefore, it takes time to stabilize the pressure, and since this manual valve operation needs to be performed with a large number of pressure set values by changing the planned pressure, it is continuously performed for a long time (usually about 10 hours). Since it had to be done, the burden on the operator was very heavy.

As a device that can partially solve such a problem, a constant-pressure water permeation test device using a closed tank has been proposed (see Japanese Patent Laid-Open No. 1-182735). this is,
The bottom of the closed tank and the inside of the injection pipe are connected by a liquid supply pipe, one end of the liquid level setting air supply hose is connected to the upper part of the closed tank, and the other end is vertically movably inserted into the injection pipe. The liquid level in the injection pipe is controlled to be constant so that the test water head to the water permeability test section is constant.

[0006]

The above-mentioned constant pressure water permeation test device can certainly perform measurement in a low water pressure state even on weak ground. However, since it is a constant pressure device, it is basically a pressure control method as in the conventional technology, and in order to change the pressure setting value, the laborious work of moving the level sensor and the air supply hose up and down in the boring hole is required. Will be needed. This task becomes quite difficult, especially at deeper depths.

The test pressure (test head) that can be applied is the head pressure from the pressure sensor mounting position to the water level of the injection pipe. The water head pressure from the water level in the injection pipe to the water level in the closed tank is below atmospheric pressure (the sum of this water head pressure and the pressure inside the closed tank is in equilibrium with atmospheric pressure), and exceeds the atmospheric pressure. I can't. That is, the depth from the water level in the closed tank to the water level in the injection pipe is about 10 m.
Must be: Therefore, in order to start the water permeability test from a low water pressure below atmospheric pressure, the measurable ground is limited to shallow ground with a depth of about 10 m or less, and cannot be performed at a depth of several tens of m or more. If the depth is deep, a large test water pressure will act from the beginning of the test, causing problems similar to the conventional one such as ground destruction. Moreover, the variable range of the test pressure that can be applied is 0 to 0 in terms of water head.
It is up to 10 m and the test pressure cannot be changed over a wider range.

Further, since this test apparatus has a limited tank capacity, it is not possible to inject a large amount of water into the boring hole, and if the tank is made larger, the test preparation work such as carrying in and installing the tank is extremely large. Becomes The planned construction site of the dam is work in the mountains, and simple equipment is required.

The object of the present invention is to make it possible to perform an accurate water permeability test even on the ground where the critical pressure is small, and to apply it even if the depth of the test section is deep, and the test pressure range is wide, and the system is simplified and miniaturized. An object of the present invention is to provide a water permeation test device that can perform automatic measurement.

[0010]

The present invention is directed to a packer for setting a water permeability test section in a borehole formed in the ground, a pressure sensor installed in the water permeability test section, and a ground surface to the water permeability test section. The water flow passage for sending water to, the pressure water supply source connected to the water flow passage, the flow meter and the flow control valve provided in the middle of the water flow passage, and the detected flow rate of the flow meter is compared with the set flow rate, and both match. Thus, the water permeation test apparatus includes a flow rate control unit for controlling the flow rate control valve and a flow rate / pressure recording unit for recording the flow rate and pressure. The characteristic of this device is that it adopts a flow rate control system, unlike the prior art. Here, the flow rate control method is a method of injecting water at a preset flow rate and measuring the pressure corresponding to that flow rate, on the assumption that the water pressure also becomes a certain constant value if water is kept constant for a unit time. .

With the above-mentioned structure, the pressure water supply source may be a combination of a pump and a pulsation prevention tank, but a hydrostatic pressure tank is preferable especially at low water pressure. Therefore, after all, these two types of pressure water supply sources are selectively used. The structure which does is most preferable. For example, an electromagnetic type is preferably used as the flow meter, and an air-driven type is preferably used as the flow rate control valve. It is desirable to install a pair of these flow meters and flow rate control valves in parallel for a small flow rate and a large flow rate depending on the flow rate range that can be measured and adjusted.

[0012]

In the present invention, the flow rate of water injection is measured by the flow meter and automatically controlled by the flow rate control valve so that it will be a predetermined constant value. Then, the pressure in the water permeability test section with respect to the flow rate is measured by a pressure sensor. Over time, the pressure measurement value approaches a certain value, so record that value. Then, the flow rate is changed and the same pressure measurement is continued. By observing and recording pressure values for many flow rates in this manner, the Lugeon value and the hydraulic conductivity of the ground can be obtained.

The device of the present invention is of a flow control type. Since the flow rate is the same everywhere in the water supply system, it is not necessary to consider the time lag like in pressure measurement. If the flow rate value to be measured is input in advance, the flow rate is automatically controlled, so that all the tests can be performed automatically.

[0014]

EXAMPLE FIG. 1 is a block diagram showing an example of a water permeability test apparatus according to the present invention. The water injection pipe 14 is inserted from the ground surface to a predetermined depth in the boring hole 12 formed in the ground 10. A packer 16 is provided on the outer periphery of the lower portion of the water injection pipe 14, and the packer 16 can be expanded by nitrogen gas supplied from a nitrogen cylinder 18 installed on the surface of the ground, and the expansion results in a permeability test section A in the boring hole 12. Set.
Further, a pressure sensor 20 is attached to the packer 16, detects the pressure in the water permeability test section, and the wiring of the pressure signal is drawn to the surface of the earth.

On the surface of the earth, various devices for feeding water from the ground into the water permeability test section and a control device therefor are installed. Connect a pressure water supply source to the base end of the water supply pipe (shown by the thick line).
This pressure water supply source is composed of two types, a combination of a pump 22 and a pulsation prevention tank 24, and a hydrostatic pressure tank 26.
Water supply from these pressure water supply sources can be switched or shut off by stop valves provided at various places. The pulsation prevention tank 24 reduces the pulsation of water discharged from the pump 22 by the air inside thereof acting as an air cushion.

The flow rate is controlled by the flowmeters 30a and 30b and the flow rate control valves 32a, which are provided in parallel in two systems in the middle of the water supply pipe.
32b. Here, the flow meter 30a and the flow rate control valve 32a of the first system are for a small flow rate (for example, 0 to 5 liters / minute), so that water from the pump 22 or water from the hydrostatic tank 26 may pass through. Has become. On the other hand, the flow meter 30b and the flow rate control valve 32b of the second system are for a large flow rate (for example, 5 to 50 liters / minute), and the pump 2
The water from 2 passes through. By installing these two systems, accurate measurement and control are possible over a wide flow range. Both flowmeters 30a and 30b are electromagnetic type, and the flow rate control valves 32a and 32b are air driven type. With this electromagnetic flow meter, a minimum reading of 10 cc / min is possible, and accurate control is possible even with a minute flow rate. Particularly in the case of an electromagnetic flow meter, accurate measurement is premised on the fact that the inside of the pipe is filled with a conductive fluid, so it is necessary to provide the flow meter upstream of the flow control valve as shown in the figure.

The flow rate signals detected by the flow meters 30a and 30b are
It is sent to the flow rate controller 34. The flow rate adjusting unit 34 compares the detected flow rate with a set flow rate and controls the opening / closing degree of the flow rate adjusting valves 32a and 32b so that they match. The detected flow rate and the pressure from the pressure sensor 20 are recorded by the flow rate / pressure recording unit 36. The power supply required for each of these parts is the generator 4
Compressed air supplied from 0 and driving the flow rate control valves 32a and 32b is supplied from the compressor 42. The flow rate adjusting unit 34 includes a flow rate setting dial, a flow rate display digital meter, and the like, can input the set flow rate, and has a function of displaying the actually measured flow rate together with the set flow rate. The flow rate / pressure recording unit 36 is equipped with a printer and a digital meter for pressure display. Both the flow rate measurement value and the pressure measurement value are output by the printer every one minute, and are recorded on a floppy disk or the like as necessary.

When the flow rate of water injection is small, the first system (flow meter 30a and flow rate adjusting valve 32a) is used, and water is injected from the hydrostatic tank 26 within a possible range. This is because the injection of water from the hydrostatic tank has no pulsation. If the flow rate of water injection is high, the second system will be used. In any case, the flow control valve is automatically closed in the unused system.

The measurement procedure is as follows. Operate the system changeover switch on the control panel to select the first system. Then, use the flow rate adjustment dial to set the flow rate control unit 3
Set an arbitrary flow rate to 4. Simultaneously with the setting of the flow rate, the flow rate control valve 32a operates, and the water injection into the water permeability test section A divided by the packer 16 starts. The water level of the water injection pipe 14 in the boring hole 12 gradually rises, and when the water injection amount and the water permeation amount are well balanced, the water level increase stops and the water pressure stabilizes. From this point, the flow rate and water injection pressure are measured and recorded every minute for 10 minutes. After the measurement for 10 minutes, the flow rate of the next stage is set with the flow rate adjusting dial, and the above procedure is repeated. When the water injection flow rate exceeds 5 liters / minute, the system changeover switch is operated to switch to the second system, the flow rate is set, and the above procedure is repeated. If the ground in the permeability test section is destroyed,
Or continue until the water injection pressure reaches 10 kgf / cm ² . Further, the packer is moved to reset the water permeability test section, and the above tests 1 to 3 are performed.

An example of the test results is shown in FIG. Also B
Is the result of measuring the same ground with a conventional device. In both cases, the analysis results are shown as a pressure-water injection flow rate curve. In the prior art, the rock mass was destroyed by the water head pressure from the groundwater level to the surface, and the critical pressure could not be measured, but in the present invention, it is possible to measure at a low water pressure and low flow rate below the critical pressure, and accurate It turns out that the Lugeon value can be obtained.

The preferred embodiment of the present invention has been described above in detail, but the present invention is not limited to this configuration. The flowmeter may be an electromagnetic type, an electrostatic type, an ultrasonic type, a propeller type, or any other type. If the set flow rate or the set flow rate condition is programmed in advance, it is possible to automatically measure all kinds of flow rates. Such control can be easily performed by digital control using a normal microprocessor, but if fuzzy control using a recently developed fuzzy chip is used, valve opening / closing control can be performed more smoothly. be able to.

[0022]

The present invention is a flow rate control system as described above, and controls the opening / closing degree of the flow rate control valve so that the flow rate is constant, and the flow rate can be detected from a small flow rate.
Since the same value is obtained no matter where it is measured in the water injection pipe, accurate control is possible. The prior art is a pressure control method, and especially when the water permeability test section becomes deep, the pressure adjustment did not work well, but in the present invention the measurement work becomes extremely easy, and the time required for the test can be greatly shortened, and the operator's The burden is reduced. By the way, according to the present invention, the test time, which takes an average of about 10 hours per site in the prior art, is 60 hours.
As a result of carrying out at more than one place, most of the measurements were completed within 1.5 hours (within 4 hours even in exceptional cases (4 places)). Further, in the present invention, since the measurement can be performed automatically, the burden of valve operation is eliminated.

In the present invention, the test section can be applied regardless of the depth, whether it is shallow or deep, and it can be applied not only to low water pressure but also to high water pressure. In addition, if the flow rate setting is programmed in advance, fully automatic measurement is possible. In addition, the device configuration is simplified and downsized, so it is easy to carry in and install at the measurement point.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a water permeability test apparatus according to the present invention.

FIG. 2 is a graph showing an example of measurement results of the present invention and the prior art.

[Explanation of symbols]

 10 Ground 12 Boring Hole 14 Water Injection Pipe 16 Packer 18 Nitrogen Cylinder 20 Pressure Sensor 22 Pump 24 Pulsation Prevention Tank 26 Hydrostatic Tank 30a, 30b Flow Meter 32a, 32b Flow Control Valve 34 Flow Control Section 36 Flow / Pressure Recording Section

Claims (3)

[Claims] 1. A packer for setting a water permeation test section in a borehole formed in the ground, a pressure sensor installed in the water permeation test section, and a water passage for supplying water from the ground into the water permeation test section. , A pressure water supply source connected to the water supply passage, a flow meter and a flow control valve provided in the middle of the water supply passage, and the flow control valve is set so that the detected flow rate of the flow meter is compared with a set flow rate so that they match. A water permeation test device equipped with a flow rate control unit for controlling and a flow rate / pressure recording unit for recording flow rate and pressure. 2. The apparatus according to claim 1, wherein the pressure water supply source comprises a combination of a pump and a pulsation prevention tank, or two of them, a hydrostatic pressure tank. 3. The flowmeter is an electromagnetic type, the flow rate control valve is an air drive type, and a plurality of pairs of the flowmeter and the flow rate control valve are arranged in parallel according to a measurable / adjustable flow rate range. The device according to claim 1 or 2, wherein