JPH0657933B2 - Water permeability test equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a hydrostatic pressure test apparatus applied to geological surveys of dams, basic grouting effect determination, etc., and particularly uses a borehole. The present invention relates to a water permeability test apparatus that applies hydrostatic pressure to check the water permeability of the ground.

[Conventional technology]

The purpose of the permeability test (Lugeon test) is to evaluate the permeability of the foundation ground of the dam.

Leakage from the dam's foundation ground not only reduces water storage efficiency, but is also an important issue regarding the safety of foundations and dams. Therefore, when constructing a dam, it is necessary to grasp the permeability of the foundation ground, which is an important test item. Further, the water permeability evaluated by the Lugeon test is also used for selecting the construction position of the dam, determining the excavation line, planning the grouting, and judging the result of the grouting.

2. Description of the Related Art Conventionally, as the water permeability test apparatus applied to the above purpose, the system shown in FIG. 2 is known.

In the figure, a test hole of a required depth (hole diameter is 66 mm in principle) 2 is vertically drilled in the ground 1 by fresh water digging, and the test hole 2 is injected from the hole mouth to reach the test section (about 5 m). Water is stopped in the test section by inserting the tube 3 and interposing the air packer 4 between the inner circumference of the lower end portion of the injection tube 3 and the inner wall of the test hole 2.

Further, a pump 7 is connected to the upper end of the injection pipe 3 projecting from the test hole 2 to the ground via a flow meter 5 and a valve 6 capable of self-recording, and a pressure gauge 8 capable of self-recording the injection pressure is provided. It is connected.

In the water permeation test apparatus having the above-described structure, the water permeation test (Lugeon test) is performed by driving the pump 7 and the valve 6
Is opened to inject water from the injection pipe 3 into the test section of the test hole 2, and pressurized water, that is, injection pressure is applied to the test section to make a constant water pressure state, and a water permeability test of the test section is performed.

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

P = P ₀ + γw (h ₁ −h ₂ −h ₃ ) (kgf / cm ² ) where P ₀ : pressure at the mouth of the injection tube h ₁ : elevation difference from the pressure gauge to the center of the test section (m) h ₂ : Head from the groundwater level L to the center of the test section (m) h ₃ : Head loss due to resistance in the injection pipe (m) γw: Unit volume weight of water Injection pressure to the test section by driving the pump 7 in this way Is applied from the ground, and the pressure is gradually changed from low pressure to high pressure, and a constant water level is obtained each time, and a permeability test is conducted for the test section. From the test results, the test section shown in Fig. 3 Create injection pressure-injection volume curve,
The Lugeon value Lu is obtained from this injection pressure-injection amount curve.
This Lugeon value refers to the injection amount when the injection pressure is 10 kgf / cm ² . Further, the above-mentioned curve is an important material not only for obtaining the Lugeon value but also for obtaining the limit pressure, and for knowing the water permeability characteristics of the ground and the reliability of the test.

The limit pressure is the pouring force at the point where the injection amount increases rapidly in the injection pressure-injection amount curve.This is because the fine water filling the fissures in the ground flows due to pressure water, or the fissures in the ground expand. It is a phenomenon that occurs when the grouting is performed, and it is an important index for knowing the water permeability characteristics of the ground and determining the grouting injection pressure.

[Problems to be Solved by the Invention]

In the above-described conventional water permeability test apparatus, the pump 7 is used to perform a stepwise test of pressure from the ground, so when the groundwater level is low, the total water pressure applied to the test section will be reduced from the ground surface. The hydrostatic head up to the groundwater level L is included. Therefore, even if the water pressure by the pump is 0, the hydrostatic head acts on the test section as pre-pressure, and the permeability test is started from a stage lower than this hydrostatic head. I can't do it.

In general, the permeability test is the limit pressure of the ground (water pressure resistance).
Since the purpose is to obtain the Lugeon value or permeability of the ground below, if the critical pressure of the target ground (geology) is smaller than the hydrostatic head from the ground surface to the groundwater level L, In the pressure stage, the test pressure exceeded the critical pressure of the ground and yielded the ground, and there was a problem that the correct Lugeon value or hydraulic conductivity peculiar to the ground could not be obtained.

The present invention solves the above problem, and an object of the present invention is to provide a water permeability test apparatus that can accurately determine the Lugeon value peculiar to the ground regardless of the groundwater level even when the critical pressure of the test ground is small.

[Means for Solving the Problems]

The water permeation test device of the present invention is a packer for forming a water permeation test section in a test hole bored in the ground, and a liquid is inserted into the test hole so as to communicate with the test section through the packer. An injection pipe, a level sensor arranged vertically movable along the injection pipe to detect the liquid level for the test head acting on the test section, and an injection pipe so that the liquid level set by this level sensor becomes constant. Liquid flow rate adjusting valve means for controlling the fluid flow rate to the test section to make the test head to the test section constant.

[Action]

In the present invention, the liquid level for obtaining the injection pressure acting on the test section is detected by the level sensor, and the flow rate adjusting valve means is adjusted so that this liquid level becomes the set level by the level sensor. The static head enables the permeability test in the test section, and the Lugeon value peculiar to the ground can be accurately obtained regardless of the groundwater level even if the critical pressure of the test ground is small.

〔Example〕

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

FIG. 1 is a schematic configuration 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 (hole diameter is 66 mm) 2 having a required depth is vertically bored in the target ground 1 by a fresh water excavation or the like. A test section (about 5 m) is set at the lower end of the test hole 2, and an air packer 10 for stopping water upward is installed in the test hole 2 located at the upper end of the test section. One end of a packer 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. Air is supplied to the air packer 10 from this air source. The test section is isolated from the non-test section by supplying and expanding it.

An injection pipe (outer diameter 44.5 mm, inner diameter 34.9 mm) 12 reaching from the ground to the air packer 10 is inserted and installed in the test hole 2, and a reducer 13 connected to a lower end of the injection pipe 12 penetrates the air packer 10 to perform a test. While being communicated with the section,
A thin flex injection hose 14 is inserted into the injection pipe 12, one end of which reaches a position close to the reducer 13, and the protruding end of the hose on the ground has a flow meter 15 and a manual flow rate adjusting valve 16. Water is supplied to the storage tank 17 via a valve 18 from a water source (not shown). Also,
A level sensor 19 for detecting the level of water for hydrostatic pressure supplied through the water injection hose 14 is arranged in the injection pipe 12, and the level sensor 19 is provided above the injection pipe 12 by a signal cable 20 connected thereto. The cable 20 is supported in a suspended state, and the ground end side of the cable 20 is connected to the measuring instrument 21.

A pressure sensor 22 for detecting the effective injection pressure at the intermediate position is arranged in the test section.
The injection pipe 1 by means of the signal cable 23 connected to it.
2 is suspended from above and the cable 23
The ground end side of is connected to the measuring instrument 21. Reference numeral 24 is a recorder for recording the detection values of the level sensor 19 and the pressure sensor 22. The groundwater level WL in this example
Is below the test hole 2.

Next, a test operation by the water permeation test apparatus of the present embodiment configured as described above will be described.

In the water permeability test, the air packer 10, the injection pipe 12 and the water injection hose 14 are installed in the state shown in FIG.

Next, when testing the test section from the level at which the water permeability test head is 0, the level sensor 19 is lowered to the central portion of the test section that coincides with the pressure sensor 22 as shown by the phantom line, and the pressure sensor 22 is further tested. Suspend and hold in the center of the.

In this state, the water source valve 18 is opened and the storage tank 17 is opened.
While pouring water into the inside, the flow rate adjusting valve 16 is opened, and the water in the storage tank 17 is injected into the test section through the injection hose 14. At this time, the water level injected into the test section reaches the level sensor 19, and when the level sensor 19 detects the water level, the water level signal is supplied to the measuring instrument 21 through the cable 20, and the current water level of the measuring instrument 21 is detected. It is displayed on the water level indicator 21a. Therefore, the operator must cover the amount of water leaking from the test section so that the water level in the test section is level sensor 1.
The flow rate adjusting valve 16 is adjusted so as to be constant at the test head (= 0) set by 9. Then, it is confirmed by observing the water level indicator 21a that the water level has become constant, and the injection pressure and the flow rate at that time are recorded by the recorder 24. The injection pressure is detected by the pressure sensor 22, and the detection signal is sent through the cable 23 to the measuring instrument 2
It is displayed on the pressure indicator 21b by adding 1 to it.

When the water permeation test with the test head = 0 is completed, the level sensor 19 is raised stepwise, for example, the head is 1, 3, 5, 7, 10 m, and each time the level sensor 19 is brought to the above-mentioned constant water level state. Then, measure and record the pressure and flow rate at that time.

When all the tests at each head level for the test section have been completed, an injection pressure-unit injection flow rate curve (a curve similar to that shown in FIG. 3) is created, and from this graph, the limit pressure and Calculate the Lugeon value.

In the present embodiment as described above, since the test method is to generate the hydrostatic head for the test section only within the hole, it is possible to perform the permeability test of the test section even from the head of 0 regardless of the groundwater level. Therefore, even if the critical pressure of the target ground (geology) is smaller than the hydrostatic head from the ground surface to the groundwater level, the correct Lugeon value and critical pressure peculiar to the ground can be obtained.

Further, by inserting the pressure sensor 22, the actual pressure in the test section can be measured, the effective injection pressure can be obtained, and the level sensor 19 can be used as a means for measuring the groundwater level (the groundwater level is tested). If it is shallower than the interval, the effective injection pressure can be obtained from the values of both the pressure sensor 22 and the level sensor 19.

In addition, in the above-mentioned example, the case of utilizing for the injection pressure generation of the test section was described, but if muddy water other than water or other highly viscous liquid is used, the amount of liquid used in the test can be small, It is suitable for ground surveys in places with poor flights.

Further, in the above embodiment, the case where the flow rate adjusting valve is manually operated has been described, but the constant water level may be automatically controlled by using an electric flow rate adjusting valve or the like. Further, the flow rate adjusting valve may be provided at the lower end of the water injection hose 12.

〔The invention's effect〕

As described above, according to the present invention, the packer and the injection pipe are inserted and installed at the upper end of the test section in the test hole bored to a predetermined depth, and the liquid level for the test head acting on the test section is detected. A level sensor is arranged so that it can move up and down along the inside of the injection pipe, and a pressure sensor that detects the injection pressure in the test section is provided, and the liquid flow rate to the injection pipe is adjusted so that the liquid level set by the level sensor becomes constant. Since the liquid flow rate adjusting valve means for controlling the test head to the test section to be constant is provided in the liquid supply path,
Permeability test of the test section is possible even from the water head of 0 regardless of the groundwater level. With this, even if the critical pressure of the ground to be tested is small, the Lugeon value peculiar to the ground can be accurately obtained. is there.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a water permeability test apparatus of the present invention, FIG. 2 is a schematic configuration diagram of a conventional water permeability test apparatus, and FIG. 3 is a graph showing a relationship between injection pressure and injection amount. 1 …… Ground 2 …… Test hole 10 …… Air packer 12 …… Injection tube 14 …… Injection hose 15 …… Flow meter 16 …… Flow rate adjusting valve 17 …… Storage tank 19 …… Level sensor 21 …… Measuring instrument 22 ... Pressure sensor 24 ... Recorder.

Claims (1)

[Claims] 1. A packer for forming a water permeation test section in a test hole bored in the ground, and an injection pipe inserted into the test hole so as to communicate with the test section through the packer and supplying a liquid to the test section. , A level sensor that is arranged so that it can move up and down along this injection pipe and that detects the liquid level for the test head that acts on the test section, and the fluid to the injection pipe so that the liquid level set by this level sensor becomes constant A water permeability test apparatus comprising: a liquid flow rate adjusting valve means for controlling a flow rate to make a test water head to a test section constant.