JPH01182735A - Apparatus for testing water permeability - Google Patents

Abstract

PURPOSE:To obtain a lugeon value inherent to the ground regardless of the level of ground water, by controlling a liquid level with a tightly closed tank on the ground, a feeding pipe, which is connected to the tank and inserted into an injecting pipe, and air feeding pipe, so that the liquid level becomes constant. CONSTITUTION:An air packer 10 forms a permeability testing section (a) in a test hole 2, which is obtained by boring the ground. An injecting pipe 12 is inserted and provided in the test hole 2 through the packer 10 so that the pipe 12 is communicated with the test section. Liquid is supplied into the test section. Injecting liquid is stored in a tightly closed tank 14 on the ground. A fluid feeding pipe 18 is connected to the lower part of the tank 14 and also inserted into the injecting pipe 12. One end of a liquid-level setting air feeding hose 20 is communicated to the upper part of the tank 14. The other end of the hose 20 is inserted into the injecting pipe 12 so that the hose can be moved up and down. The hose 20 adjusts the flow rate of the liquid, which is injected through the feeding pipe 18 so that a testing water head (b) in the test section becomes constant. The liquid level in the injecting pipe 12 is controlled at a constant level. The water level is detected with a level sensor 21 and displayed on a measuring device 23 together with injecting pressure, which is detected with a pressure sensor 22.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a hydrostatic permeability test device that is applied to geological surveys of dams, etc., basic grouting effect evaluation, etc. , relates to a permeability test device that tests the permeability of the ground by applying hydrostatic pressure.

[Conventional technology]

The purpose of the water permeability test (°Luzion test) is to evaluate the permeability of the foundation ground of a dam.

Water leakage from the foundation of a dam not only reduces water storage efficiency, but also poses an important problem concerning the safety of the foundation and dam body. Therefore, when constructing a dam, it is necessary to understand the permeability of the foundation ground, which is an important test item. In addition, the permeability and other properties evaluated by the Lugeon test are used to select the location for dam construction, determine excavation lines, plan grouting, and judge the results of grouting.

BACKGROUND ART Conventionally, a system shown in FIG. 2 has been known as a water permeability test device applied to the above-mentioned purpose.

In Fig. 2, a test hole 2 of the required depth (hole diameter is 66 mm in principle) is vertically excavated in the ground 1 using fresh water drilling, and inside this test hole 2 there is a hole between the hole opening and the test zone (55 mm). - m) is inserted, and an air packer 4 is interposed between the outer periphery of the lower end of the injection pipe 3 and the inner wall of the test hole 2 to shut off water in the test section.

In addition, a pump 7 is connected to the upper end of the injection pipe 3 protruding above the ground from the test hole 2 via a flow meter 5 and a pulp 6 that display the amount of water to be injected, as well as an injection pressure (mouth pressure).
A pressure gauge 8 that displays .

In the water permeability test device having the above configuration, during the water permeability test (Lugeon test), the pump 7 is driven and the valve 6 is
After opening, water is injected from the injection pipe 3 into the test section of the test hole 2, pressure water, that is, injection pressure is applied to the test section, and a water permeability test is conducted in the test section under a constant water pressure state.

At this time, the effective injection pressure P acting on the test section is expressed by the following equation.

P=Po +yw(hl hz hs) (K
gf/c1iI) However, Po: Pressure at the mouth of the injection pipe;: Difference in elevation from the pressure gauge to the center of the test section (m); hl: Water head from the groundwater level to the center of the test section (m);
) hs: Head loss due to resistance in the injection pipe (m) γ-: Unit volume weight of water In this way, by driving the pump 7, injection pressure is applied from the ground to the test section, and the pressure is changed from low pressure to high pressure. The transition is carried out step by step, and a water permeability test is carried out in the test section each time with a constant water level. Based on the test results, an injection pressure car injection amount curve for the test section as shown in Figure 3 is created, and this injection pressure car The Lugeon value u is determined from the injection dose curve. This Lugeon value refers to the injection amount when the injection pressure is 10 Kgf/al. In addition, the above curve is an important document not only for determining the Lugeon value but also for determining the critical pressure and knowing the permeability characteristics of the ground and the reliability of the test.

The critical pressure is the injection pressure at the point on the injection pressure car injection amount curve where the injection amount suddenly increases. This is a phenomenon that occurs when the grouting occurs, and is an important indicator for understanding the permeability characteristics of the ground and determining the injection pressure for grouting.

[Problem to be solved by the invention]

In the conventional water permeability test equipment described above, the pump 7 is used to perform the test by applying pressure from the ground in stages, so if the groundwater level is low, the groundwater will not be included in the total water pressure applied to the test section. It includes the static water head from the surface to the groundwater level, so even if the water pressure from the pump is 0, the static water head acts on the test section as a pressure, and water permeation starts from a stage lower than this static water head. Unable to conduct test.

Additionally, in general, water permeability tests are conducted to determine the limit pressure (water pressure resistance) of the ground.
Since the purpose is to obtain the Lugeon value or permeability coefficient of the ground in the following, the target ground (
If the critical pressure of the ground (geology) is smaller than the hydrostatic head from the ground surface to the groundwater level, the test pressure exceeds the critical pressure of the ground in the buri pressure stage, causing the ground to yield, and the correct Lugeon value or hydraulic conductivity unique to the ground is determined. There was a problem that I could not ask for.

The present invention solves the above problem, and aims to provide a permeability testing device that can accurately determine the Lugeon value specific to the ground regardless of the groundwater level even when the critical pressure of the ground to be tested is small.

[Means to solve the problem]

The permeability test device of the present invention includes a packer for forming a permeability test section in a test hole bored in the ground, and a packer inserted into the test hole so as to communicate with the test section through the packer to supply liquid to the test section. an injection pipe, a sealed tank for storing injection liquid, a liquid supply pipe that communicates between the bottom of the sealed tank and the inside of the injection pipe, one end communicating with the top of the sealed tank and the other end extending vertically into the injection pipe. A liquid level setting air supply hose is movably inserted and controls the liquid level in the injection pipe to be constant so that the test water head to the test section is constant.

[For production]

In the present invention, the liquid level for obtaining the injection pressure acting on the test section is controlled to be constant by an above-ground sealed tank, a supply pipe connected to the tank, and a supply pipe and air supply hose inserted into the injection pipe. , it becomes possible to supply a flow rate that is balanced with water permeability while maintaining a constant water head.
It is possible to perform a permeability test in the test section using the hydrostatic head obtained in the hole, and even when the critical pressure of the test ground is small, the Lugeon value specific to the ground can be accurately determined regardless of the groundwater level.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a water permeability test apparatus to which the method of the present invention is applied.

In the figure, a test hole 2 of the required depth (hole diameter: 66 mm) is vertically bored in the target ground l by clear water drilling or the like. There is a test section (approximately 5m) at the lower end of test hole 2.
An air packer 10 is installed in the test hole 2, which is located at the upper end of this test section, to stop water from flowing upward. One end of a backer air tube 11 is connected to the air packer 10, and the other end is connected to an air source (not shown) such as a compressor installed on the ground, and air is supplied to the air packer 10 from this air source. The test area is separated from the non-test area by inflating the test area.

Inside the test hole 2 is an injection pipe (outer diameter 44.5 mm, inner diameter 34.9 mm) that reaches the air packer 10 from the ground.
12 is inserted and installed, and the reducer 1 is connected to its lower end.
3 passes through the air packer 10 and communicates with the test section.

A closed tank 14 for storing water for injection is installed near the test hole on the ground, and water can be supplied into this closed tank 14 from a water source via an openable pulp 15. One end of a water supply pipe 18 is connected to the water supply pipe 18 via an open/close pulp 16 and a flow meter 17.
The other end side is extended to a position close to the reducer 13 within the injection pipe 12 . In addition, the sealed tank 14
One end of an air supply hose 20 for setting the water level is connected to the upper end via an opening/closing pulp 19, and the other end is inserted into the injection pipe 12 so as to be movable up and down.

Reference numeral 21 denotes a level sensor for detecting the water level disposed inside the injection pipe 12. This level sensor 21 is suspended from above the injection pipe 12 by a signal cable 22 connected to the level sensor 21, and is connected to the ground side of the cable 22. The end is connected to a measuring device 23. Further, 24 is a pressure sensor for detecting injection pressure located at the center of the test section in the test hole 2, and this pressure sensor 24 is connected to the injection pipe 12 from above by a signal cable 25 connected thereto. The cable 25 is supported in a suspended state, and the ground side end of the cable 25 is connected to the measuring instrument 23 . 26 is a recorder for recording the detected values of the level sensor 21 and pressure sensor 24. In this example, it is assumed that the groundwater level WL is below the test hole 2.

Next, a test operation using the water permeability test apparatus of this embodiment configured as described above will be explained.

For the water permeability test, use Air Packer 10. The injection pipe 12 and the supply pipe 18 are installed in the state shown in FIG.

Next, when testing the test section from the level where the water permeability test water head is 0, lower the lower ends of the level sensor 21 and the air supply hose 20 to the center of the test section, which coincides with the pressure sensor 24, as shown in the imaginary line, Furthermore, the pressure sensor 24 is suspended and held at the center of the test section.

In this state, the valve 19 is opened to expose the upper end of the sealed tank 14 to the atmosphere (inside the test hole 2) through the air supply hose 20, and the pulp 16 is opened to allow water in the sealed tank 14 to pass through the supply pipe 18. Inject into the test section. At this time, the water level injected into the test section was
When the pressure reaches a level that closes the 0 opening, the upper space in the sealed tank 14 becomes vacuum pressure, and water injection into the test section is thereby stopped.

On the other hand, since the inner wall of the test section is permeable, the injected water permeates through it, and when the water level drops accordingly and the lower end of the air supply hose 20 is opened, water is injected through the supply pipe 18 again. Ru. As a result, the water level in the test section is controlled to be constant at the test water head (=0) set by the air supply hose 2o. The water level at this time is detected by the level sensor 21, and by adding the detection signal to the measuring device 23, it is displayed on the water level indicator 23a.
It is confirmed by looking at the water level indicator 23a that the water level has become constant, and the recorder 26 records the injection pressure and the flow rate detected by the flow meter 17 at that time. Further, the injection pressure is detected by the pressure sensor 24, and the detection signal is applied to the measuring device 23 through the cable 25, thereby being displayed on the pressure indicator 23b.

After the water permeability test with the test water head = 0 is completed, the level sensor 21 and the lower end opening of the air supply hose 20 are raised stepwise, for example, to a water head of 1.3, 5, 7.10 m, each time. , set the water level to the above-mentioned constant state, and measure the pressure and flow rate at that time.

Record.

Once all tests have been completed at each water head level for the test section, create an injection pressure car unit injection amount curve (similar to the one shown in Figure 3), and use this graph to calculate the limit pressure as in the conventional method. Find the Lugeon value.

In this example as described above, since the test method is to generate a static head for the test section only inside the hole, it is possible to conduct a permeability test for the test section even from a water head of 0 regardless of the groundwater level. , the ground (geology) that will be subject to this
Even if the critical pressure is smaller than the hydrostatic head from the ground surface to the groundwater level, the correct Lugeon value and critical pressure specific to the ground can be determined.

Furthermore, by inserting the pressure sensor 24, the actual pressure in the test section can be measured, and the effective water injection pressure can also be determined, and the level sensor 21 can also be used as a means for measuring the underground water level. Furthermore, since a constant water level is obtained by utilizing the natural phenomenon caused by the vacuum effect using the closed tank 14, there is an effect that the injection equipment can be simplified.

In addition, in the above example, a case was described in which water was used to generate injection pressure in the test section, but if muddy water or other highly viscous liquid other than water is used, the amount of liquid used during the test can be reduced. Suitable for ground investigation in places with poor access to water.

[Effects of the Invention] As described above, according to the present invention, a packer and an injection pipe are inserted and installed at the upper end of a test section in a test hole bored to a predetermined depth, and the packer and injection pipe are installed on the hole side. A liquid supply pipe connected to the bottom of the sealed tank for liquid storage is inserted into the injection pipe, and an air supply hose for setting the liquid level, which is connected to the top of the sealed tank, is inserted into the injection pipe so as to be movable up and down.
The test water head acting on the test section is maintained constant by the vacuum pressure generated in the sealed tank, and a flow rate that is balanced with the water permeability can be supplied in a timely manner, so regardless of the groundwater level, zero It is now possible to test the permeability of the test section even from the water head, and as a result, even if the critical pressure of the ground to be tested is small, it is possible to accurately determine the Lugeon value specific to the ground. Furthermore, since a sealed tank is used and constant level control is performed by natural flow due to the vacuum effect of the tank, the injection mechanism is simplified.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an example of a water permeability testing device of the present invention, FIG. 2 is a schematic diagram of a conventional water permeability testing device, and FIG. 3 is a graph showing the relationship between injection pressure and injection flow rate. l...Ground 2...Test hole 10...Air packer 12...Injection pipe 14...Sealed tank 4 1 day... ... Supply pipe 20 ... Air supply hose 21 ... Level sensor 23 ... Measuring device 24 ... Pressure sensor 26 ... Recorder . Effective main thrust force (kgf/cm2)

Claims (1)

[Claims] (1) A packer for forming a permeability test section in a test hole bored into the ground, an injection pipe inserted into the test hole so as to communicate with the test section through the packer, and supplying liquid to the test section; a sealed tank for storing a liquid; a liquid supply pipe communicating between the bottom of the sealed tank and the inside of the injection pipe; one end communicating with the upper part of the sealed tank and the other end vertically movably inserted into the injection pipe; and a liquid level setting air supply hose that controls the liquid level in the injection pipe to be constant so that the test water head to the test section is constant.