JP3065208B2 - On-site permeability test equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a water permeability test in which the water level in an airtight pipe is adjusted using gas pressure. More specifically, the present invention combines a method of connecting a gas-tight pipe to a packer for setting a test section, changing a water level in the gas-tight pipe by gas pressure, and a method of detecting a test section pressure by a pressure sensor,
In a device that determines the permeability of the formation from the change over time in the detected pressure, a shut-off valve is installed in the airtight pipe, and the shut-off valve is closed so that the equilibrium water level (water head) can be measured in a short time. It is about technology.

[0002] This in-situ permeability test is useful in the field of groundwater investigation in which a borehole is excavated in a stratum prior to various civil engineering construction works or according to various scientific requirements. In particular, it is effective for an in-situ permeability test in a poorly permeable stratum having a permeability coefficient k of the order of 10 ⁻⁵ cm / sec or less.

[0003]

2. Description of the Related Art As a conventional technique for determining the permeability of a formation, there is a method called a JFT test. For this, a packer with a trip valve at the upper end of a water pipe running through the center is used. A pipe reaching the ground is connected to the packer and lowered to a predetermined depth in the borehole. At that time, the trip valve is kept closed. Further, in order to measure the water level in the pipe, a water level detection device having a large number of electrodes arranged at predetermined intervals is inserted. After the borehole is sealed with a packer, the messenger drops from the ground and the trip valve is opened. Then, the water rises in the pipe at a speed determined by the permeability of the stratum below the packer of the borehole, and the change in the water level is measured over time with an electrode and a conductivity meter to determine the permeability.

The JFT method has been used as the only test method capable of measuring the permeability of a formation up to several tens of meters relatively accurately. However, in recent years, it has been required to measure the water permeability at a greater depth due to various circumstances, and there is a limit in meeting the demands in the JFT test in the following points. As the depth increases, it becomes difficult to open the trip valve.
Also, if a test is performed by inserting a packer into the borehole, water will enter the pipe. Therefore, the test cannot be performed again without taking out the pipe, closing the trip valve, and reinserting it. Since the trip valve is located immediately above the packer, the moment the valve is opened, a water pressure of approximately the same depth is generated on the borehole wall toward the inside of the hole. Therefore, the hole wall may be broken, and there is a possibility that accurate measurement cannot be performed. The change in water level can be detected by a large number of electrodes inserted into the pipe, but continuous measurement cannot be performed because the electrodes are provided at intervals. Therefore, a large measurement error occurs particularly when the rate of change of the water level is low.

[0005] Therefore, the above-mentioned drawbacks are solved, the test can be repeatedly performed without being affected by the measurement depth, the fracture of the hole wall does not occur, and the strength of the geology can be freely adjusted. As a technique that can be performed simply and with high accuracy, the present inventors have previously proposed "a method and apparatus for testing the permeability of formations" (Japanese Patent Application Laid-Open No. 2-304112). This uses a water pressure detection packer and an airtight pipe connected to it, and uses a gas pressure to change the water level in the airtight pipe,
This is a combination of a method of directly detecting a test section pressure with a pressure sensor.

[0006] The permeability test apparatus has the following configuration.
An airtight pipe is connected to the upper part of the water pipe running through the center of the packer, and the upper end is raised to the ground. A switching valve is provided at the upper part of the airtight pipe so that it can be switched to a pressurized gas source on the ground or to the atmosphere. A pressure sensor for detecting a water pressure in a test section separated by the packer and a pressure recording device for recording a detection signal thereof are provided.

First, a packer is inserted into a borehole. When the packer is inserted, the switching valve is open to the atmosphere, and the inside of the airtight pipe is at atmospheric pressure. Therefore, the water level in the airtight pipe matches the natural water level. Next, the switching valve is switched to the pressurized gas source side to apply gas pressure to the hermetic pipe, depress the water level in the hermetic pipe, and set the water level by adjusting the gas pressure. Then, the packer is inflated to make the borehole water-impervious and the test section is set. Thereafter, the switching valve is operated to open the airtight pipe to the atmospheric pressure. The test section pressure temporarily drops to almost the head inside the airtight pipe, but the water level in the airtight pipe rises in response to the supply of groundwater from the hole wall, and the test section pressure also rises accordingly. The change with time of the pressure is recorded to determine the hydraulic conductivity.

[0008]

However, in the permeability test, measurement of the equilibrium water level (head) is indispensable. This is because the measurement error of the equilibrium water level does not appear as a large error in the calculation of the hydraulic conductivity, but the hydraulic conductivity cannot be calculated unless it is determined. Even in the case of the permeability test method in which the initial water level is adjusted and determined by the gas pressure as described above,
In particular, when the formation is poorly permeable (for example, the permeability coefficient k = 1)
To 0 ^-5 cm / sec or less), it takes a very long time to the water level to reach equilibrium within the borehole, the measurement work has become extremely difficult. By the way, the permeability coefficient k is 10 ^-6 cm /
In the order of sec, it takes about two days for the equilibrium water level to be obtained. Therefore, the equilibrium water level tends to be roughly measured in the test of a poorly permeable formation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned technical problems, and to complete the measurement of the equilibrium water level in a short time even in a poorly permeable formation, and to obtain an accurate value. the working time of the entire permeability test can significantly reduce, to provide a field permeability test equipment such as high-precision measurement result is obtained.

[0010]

SUMMARY OF THE INVENTION The present invention is an in-situ permeation test apparatus for controlling the water level in an airtight pipe by using gas pressure. The main body of the water permeability test device is provided with a packer which is provided with a water pipe running through the center and is inserted into a borehole, an airtight pipe whose lower end is connected to the upper end of the water pipe and whose upper end reaches the ground. A pressurized gas source, a switching valve capable of switching the inside of the hermetic pipe to the pressurized gas source side or the atmospheric side, a pressure sensor for detecting a water pressure in a test section separated by the packer, and recording a detection signal of the pressure sensor. And a pressure recording device. The feature of the present invention is that in such a water permeability test apparatus, a cutoff valve having a structure capable of squeezing and closing a flexible tube having a water passage inside by using gas pressure from the outside is assumed when performing a water permeability test. It is installed at a position between the lowest water level in the hermetic pipe and the packer. The packer includes, for example, a water pipe running through the center, a rubber tube surrounding the outside, fixed at both ends and expandable by supply of pressurized gas, and a pressure sensor for detecting a pressure below the rubber tube. A water pressure detection packer with a structure is preferred.

The packer may have a single packer structure, and a test section may be provided between the packer and the bottom of the boring hole, or a double packer having another lower packer disposed at a predetermined interval below the packer. As a structure, a configuration may be adopted in which a test section is provided between both packers. In the case of the double packer structure, the shut-off valve is provided above the upper packer.

The shut-off valve used in the present invention is designed such that the upper and lower ends of the rubber tube are slightly expanded in the shape of a truncated cone.
An outer member having a tapered surface and an inner cylindrical member having a wedge-shaped tip are sandwiched, and concave portions are provided on the inner surfaces of both outer members, so that a cylinder is provided between the inner surface of the combined outer member and the outer surface of the rubber tube. There is a structure in which a gas chamber is formed, and a gas supply path is formed in the inner axial direction of one of the outer members to communicate an external pressurized gas source with the gas chamber. The tube is preferably made of rubber, but may be made of a soft synthetic resin.

[0013]

When pressurized gas is supplied into the hermetic pipe while the shut-off valve is kept open in the borehole, the water level in the hermetic pipe falls. The packer inflates the space between the top and bottom of the borehole by the expansion, thereby setting a test section. In the case of a single packer, the test section is between the packer and the bottom of the boring hole. In the case of a double packer, the test section is between the two packers. When the pressure in the hermetic pipe is released to the atmosphere, the pressure in the test section rapidly decreases, groundwater flows in from the stratum in the test section, and the water level in the hermetic pipe gradually increases. The pressure sensor detects the pressure at this time, and the pressure recording device records the change over time. The hydraulic conductivity is determined from the change over time in the test section pressure.

If the time-dependent change of the test section pressure is measured only while the hydraulic conductivity is determined, it is not necessary to continue the measurement thereafter. When the shut-off valve is closed, the flow of water that is going to rise in the hermetic pipe is blocked, so that no inflow of groundwater from the formation occurs, and only the test section pressure rises. This pressure rises quickly with only a small flow of water and eventually reaches a constant value. This constant value is the equilibrium head (water level) of the test section, and the pressure sensor detects this equilibrium head.

[0015]

FIG. 1 is an overall configuration diagram showing an embodiment of an on-site permeability test apparatus according to the present invention, in which a single packer is used. The main body of the water permeability test device is provided with a water pipe 10 penetrating through the center portion thereof, and a packer 14 inserted into the borehole 12, an airtight pipe 16 connected to the water pipe 10 at the lower end and reaching the upper end to the ground, An installed pressurized gas source 18 (for example, a nitrogen gas cylinder) and the hermetic pipe 16
A three-way switching valve 20 is provided which can switch the inside to the pressurized gas source side or the atmosphere side. Further, a pressure sensor 22 for detecting a water pressure in a test section divided by the packer 14 is provided, and a pressure recording device 24 is installed on the ground to record a detection signal of the pressure sensor 22.

The packer 14 is formed of a rubber tube which surrounds the outside of the water pipe 10 and is fixed at both ends and expands by the supply of pressurized gas. It is a structure that blocks water above and below the boring hole 12 at the position. Therefore, in this embodiment, the test section is between the packer 14 and the bottom of the boring hole. Here, the pressure sensor 22 is attached to the upper end of the packer 14, but communicates with the lower end of the packer 14 via a water conduit (shown by a broken line) 26 (packer 1).
4 is opened at the lower end of the packer 14), and the pressure below the packer 14 (the pressure in the test section) is detected.

According to the present invention, the shut-off valve 30 having a structure in which a flexible tube having a water passage inside can be squeezed and closed by using gas pressure from the outside is connected to an airtight pipe 16 which is assumed to be used in a water permeability test. It is installed at a position between the lowest water level in the inside and the packer 16, and is characterized in this point. Shut-off valve 3
0 is shown in FIG. The shut-off valve 30 is a rubber tube 3
Outer members 34 and 35 each having a tapered surface on its inner peripheral surface so that the vicinity of both upper and lower ends of 2 are slightly expanded in a truncated cone shape;
In this structure, the inner cylinder members 36 and 37 each having a wedge-shaped tip end are sandwiched. The upper and lower outer members 34 and 35 are airtightly screwed via an O-ring seal 38 so that both outer members 3
A concave portion 40 is provided on the inner peripheral surface of each of the outer members 3 and 4.
A cylindrical gas chamber is formed between the inner surfaces of the rubber tubes 4 and 35 and the outer surface of the rubber tube 32. The concave portion 40 has a cross-sectional shape in which the central portion is deep and the upper and lower ends are tapered and shallow. Then, a gas supply path 42 communicating with the gas chamber is formed in the axial direction of the upper outer member 34, and a connecting portion 46 for connecting a pressurized gas tube 44 (see FIG. 1).
Is provided. The external pressurizing tube 44 is connected to the on-off valve 4 on the ground side.
It is connected to a pressurized gas source 18 via 8.

Here, the rubber tube 32 uses a molded product in which both ends are slightly expanded outwardly and becomes slightly thicker toward the both ends, but has a very simple cylindrical straight shape. Is also good. 18 with respect to the center of the section
A groove (thin portion) extending in the axial direction is formed at the 0-degree symmetrical position, and is bent at the position of the groove by gas pressure from the outside to facilitate squeezing. In addition, a circumferential groove having a V-shaped cross section is formed at three places on the tapered surfaces of the outer members 34 and 35, and the outer member 34 and 35 and the inner cylindrical members 36 and 37 are used to form the rubber tube 32.
When the both ends are clamped, the rubber is cut into the circumferential groove to prevent slippage.

In the shutoff valve 30, the gas supply passage 42 is formed in the axial direction, and the connecting portion 46 is also drawn out in the axial direction. Also, since the structure is such that both ends of the rubber tube 32 are pressed obliquely with respect to the central axis using a tapered surface, the pressing margin in the radial direction may be small, and therefore the outer diameter is smaller than the inner diameter (diameter of the water passage). (For example, the outer diameter is about 54 mmφ), and it can be used in a normal small-diameter (66 mmφ) boring hole. Further, since the system is operated by a pressurized gas, unlike a solenoid valve or the like, it can be reliably and easily opened and closed even at a large depth.

The on-site permeability test method using the present apparatus will be described. The basic permeability test method may be the same as the conventional method described above. First, the packer 14 is inserted into the boring hole 12 to a predetermined depth while the shutoff valve 30 is opened and the airtight pipe 16 is kept at atmospheric pressure by the three-way switching valve 20. The test section is between the position of the packer 14 and the bottom of the boring hole. Next, the three-way switching valve 20 is operated to supply nitrogen gas from the pressurized gas source 18 into the hermetic pipe 16 to change the water level from the natural water level L ₀ to the initial water level L _{1 for the} permeability test.
Press down. This water permeability test initial water level L ₁ is located above the shutoff valve 30. Then, the packer 14 is inflated, and the space between the upper and lower portions of the boring hole 12 is made watertight at that position. As a result, a test section is set. Although not shown, the packer 14 is expanded by pressurized gas supplied from the ground through a tube or the like. The pressure sensor 22 detects the pressure in the test section, and records the change over time in the pressure with the pressure recording device 24.

FIG. 3 shows how the head (water level) detected by the pressure sensor 22 changes with time. By operating the three-way switching valve 20, the pressure in the airtight pipe 16 is released to the atmosphere. When the stratum is poorly permeable, the supply of groundwater from the hole wall is small, so that the water level in the hermetic pipe 16 is unlikely to rise, and the detected pressure value rapidly drops to near the head of the hermetic pipe 16. Then, the groundwater gradually flows in from the hole wall of the test section, and the water level in the airtight pipe 16 gradually rises, so that the pressure detected value by the pressure sensor 22 also gradually rises. The hydraulic conductivity is determined from the time-dependent change curve of the water head. And the measurement time T ₁ required is about several tens of minutes from several tens of seconds. In other words, it is sufficient if a fairly clean measurement curve can be obtained. If left untouched, the head will continue to slowly rise further toward the equilibrium head, as indicated by the dashed line. In the prior art, but is in the range had continued to measure it subsequently, in the present invention, the measurement time T ₁ after necessary for obtaining permeability may close the shut-off valve 30.

To close the shut-off valve 30, the on-off valve 48
To supply the pressurized gas into the gas chamber via the pressurized gas tube 44, the connecting portion 46, and the gas supply path 42. Due to the pressure, the rubber tube 32 is flattened from both sides and cuts off the water passage. When the shut-off valve 30 is closed in this way, the flow of water that is going to rise in the airtight pipe 16 is prevented, so that the inflow of groundwater from the stratum occurs only slightly, corresponding to the water compression rate. Only the test section pressure rises. As shown in FIG. 3, this pressure rise occurs quickly because there is almost no flow of water, and eventually becomes constant at time (time T ₂ ).
This constant pressure is nothing less than the equilibrium head (water level) of the test section. The pressure sensor 22 detects this equilibrium head. Time T ₂ to reach the equilibrium water head, is about several minutes to several tens of minutes. Therefore, the time T ₂ of the reach time T ₁ and the balance water head required for measuring these permeability, it depends on the permeability of the large and small, even combined both (T ₁ +
T ₂ ) does not exceed 2-3 hours. Note that the order of the measurement of the head change and the measurement of the equilibrium water level may be reversed.

In the example of FIG. 1, the pressure sensor 2
Since the pressure sensor 2 is provided above the packer 14, the detected pressure is based on the water pressure at the water introduction port below the packer.
The head pressure of up to 2 is reduced. However, since the length of the headrace channel is constant, its head pressure is constant, and there is no problem in terms of relative values. If necessary, a correction such as adding the head pressure may be performed.

The above-described test method is a recovery method for obtaining a change in water head (water level) when the pressure in the test section gradually recovers. It can also be used in the case of the water injection method in which the water is pumped. Further, in the above embodiment, the test section is set between the single packer and the bottom of the boring hole, but the test section is set between arbitrary points of the boring hole by the double packer. You can also. In such a case, a test section may be set by disposing a lower packer at a predetermined interval below the packer, and a shutoff valve may be provided above the upper packer.

[0025]

As described above, the present invention is conceived when performing a water permeability test on a shut-off valve having a structure in which a flexible tube having a water passage inside can be compressed and closed by using gas pressure from the outside. It is installed at a position between the lowest water level in the airtight pipe and the packer, and the equilibrium head (water level) is obtained by measuring the pressure, not the flow of the groundwater. Can be measured in a short time and an accurate value can be obtained, the time of the whole permeability test can be shortened, and the accuracy of the result can be improved. For example, if the permeability coefficient k is 10
^In the case of a stratum of about ^-6 cm / sec, in order to accurately obtain the equilibrium water level, the conventional technology required about two days,
According to the present invention, several minutes to several tens of minutes may be sufficient, and the working efficiency is significantly improved.

[Brief description of the drawings]

FIG. 1 is an overall explanatory view showing one embodiment of an on-site permeability test apparatus according to the present invention.

FIG. 2 is a structural view showing an example of a shut-off valve incorporated therein.

FIG. 3 is a graph showing an example of a relationship between a water head (water pressure) and an elapsed time in a water permeability test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Water pipe 12 Boring hole 14 Packer 16 Airtight pipe 18 Pressurized gas source 20 Three-way switching valve 22 Pressure sensor 24 Pressure recording device 26 Water conduit 30 Shut-off valve

Continuation of the front page (56) References JP-A-1-312115 (JP, A) JP-A-2-304112 (JP, A) JP-A-3-93828 (JP, U) (58) Fields surveyed (Int .Cl. ⁷ , DB name) E02D 1/00-1/08 G01V 9/02

Claims (3)

(57) [Claims] 1. A packer having a water pipe penetrating through a central part thereof and inserted into a borehole, an airtight pipe having a lower end connected to an upper end of the water pipe and an upper end reaching the ground, and a pressurized pipe installed on the ground. A gas source, a switching valve capable of switching the inside of the hermetic pipe to a pressurized gas source side or an atmosphere side, and a water permeability test.
Between the lowest water level in the airtight pipe and the packer when performing
A shut-off valve located in a pressure sensor for detecting the pressure of the test interval delimited by the packer, the permeability test apparatus and a pressure recording apparatus for recording a detection signal of the pressure sensor, the shut-off valve, an internal It is a water channel that communicates with the water pipe.
The upper and lower ends of the flexible tube are separated by an inner cylindrical member and an outer member.
Hold it so that it sandwiches the inner surface of the outer member and the flexible tube.
By introducing pressurized gas between the outside and the outside, the gas pressure from the outside
The flexible tube can be compressed and closed using force to
An on-site permeation test device characterized by a structure that opens and closes . 2. The site according to claim 1, wherein another lower packer is disposed at a predetermined interval below the packer, a test section is set by both packers, and a shut-off valve is installed above the upper packer. Permeability test equipment. 3. The flexible tube of the shut-off valve has a cross-section
Form a groove that extends in the axial direction at a 180-degree symmetric position with respect to the center
A rubber tube form, as the upper and lower end vicinity of the rubber tube is slightly flared frustoconical, outer forming a circumferential groove of a V-type to the tapered surface Chi also a tapered surface, respectively <br /> and side member, while sandwiched between the inner tubular member each having a distal end portion of the cross-section wedge-shaped, rubber tube central portions of both the outer member
A concave portion is provided on the inner surface opposite to the gas chamber, and a gas chamber is formed between the inner surface of the combined outer members and the outer surface of the rubber tube. In the axial direction of one outer member, the gas chamber is formed from an external pressurized gas source. The on-site water permeability test apparatus according to claim 1 or 2, wherein the apparatus has a structure in which a gas supply path communicating with the gas is formed.