JP2010243337A - Method for measuring pore pressure of multilayer aquifer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for measuring a pore pressure of a multilayer aquifer, which simultaneously and accurately measures the pore pressure (pressure head) of each aquifer in the multilayer aquifer, by using one boring hole without disposing any sealing layer and water shielding layer. <P>SOLUTION: In the method, the boring hole is bored in a multilayer aquifer ground so as to penetrate the multilayer aquifer, and then a depth position of each aquifer in the multilayer aquifer ground is measured in the boring operation, and a pore pressure meter is disposed in the boring hole, and a ground water current meter is disposed at a point corresponding to each aquifer depth position measured, and a water level lowering operation is carried out in the boring hole, and then a current-variation time point of the ground water in each aquifer is measured by using the ground water current meter disposed so as to correspond to each aquifer, in a lapse in which the water level is restored in the boring hole, and a water level position in the boring hole is measured at the variation time point by using the pore pressure meter, thereby measuring the pore pressure of each aquifer on the basis of the measured values. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a method for measuring pore water pressure in a multilayer aquifer.
For example, when it is necessary to determine the ground condition for various reasons, it is necessary to know the distribution of groundwater pressure. Therefore, in order to do so, each water pressure at each depth of the ground, that is, the pore water pressure must be measured.

In order to measure the pore water pressure (pressure head) of a multi-layer aquifer, drilling holes one by one for each aquifer, or by using one boring, A method of providing a measurement section isolated for each aquifer by a packer is generally known, and the pore water pressure (pressure head) is measured for each target aquifer using a water level gauge or a pore water pressure gauge.

JP-A-7-190871

By the way, in construction work involving excavation work, groundwater problems associated with ground excavation always occur. In particular, the ground in many parts of Japan has a lot of alternating layers, and therefore the ground that is the subject of excavation work is recognized as the so-called multilayer aquifer ground.
Therefore, in ground excavation work, it is first and foremost important to understand the initial head and permeability of the multi-layer aquifer.

For that purpose, it is necessary to grasp the pore water pressure (pressure head) of each aquifer, but as described above, each aquifer is sealed and cut off, and each layer is investigated. It had to be time consuming, laborious and costly.
That is, when drilling a boring hole through the multilayer aquifer ground, a water level surface (pore water pressure surface: pressure head surface) appears in the boring hole together with the drilling hole. This water level surface is the water level surface of the aquifer having the highest pore water pressure (pressure head). Therefore, in a multilayer aquifer, it is almost difficult to measure the pore water pressure (pressure head) of each aquifer unless a water shielding layer is provided for each aquifer.

Thus, the present invention provides a multi-layer belt that simultaneously and accurately measures the pore water pressure (pressure head) of each aquifer in the multi-layer aquifer without installing a seal layer or a water-impervious layer at one borehole. An object of the present invention is to provide a method for measuring the pore water pressure of an aqueous layer.

The method for measuring pore water pressure in a multilayer aquifer according to the present invention is as follows:
Drilling a boring hole through the multilayer aquifer through the multilayer aquifer, measuring the depth position of each aquifer in the multilayer aquifer after drilling,
Next, a pore water pressure meter is disposed in the borehole, and a groundwater flow meter is disposed at a corresponding position of each measured aquifer depth position,
After performing the water level lowering operation in the borehole, the groundwater flow direction of each aquifer is changed by the groundwater flow meter installed corresponding to each aquifer during the course of recovery of the water level in the borehole. Measuring the time point, measuring the position of the water level surface in the borehole at the time of the change by the pore water pressure gauge, and measuring the pore water pressure of each aquifer from the measured value,
It is characterized by
Or
Drilling a boring hole through the multilayer aquifer through the multilayer aquifer, measuring the depth position of each aquifer in the multilayer aquifer after drilling,
Next, a pore water pressure meter is disposed in the borehole, and a groundwater flow meter is disposed at a corresponding position of each measured aquifer depth position,
After performing the water level lowering operation in the borehole, during the process of recovering the water level in the borehole, the flow of groundwater in each aquifer is measured by the groundwater flow direction meter installed corresponding to each aquifer. Measuring the time point when the water is stopped and measuring the water level surface in the borehole at the time of the stop using the pore water pressure gauge, and measuring the pore water pressure of each aquifer from the measured value,
It is characterized by
Or
After performing the water level lowering operation in the boring hole, during the process of recovering the water level in the boring hole, the measurement performed was performed several times, and the measurement accuracy was improved.
It is characterized by
Or
The groundwater flow meter is a single unit, and the single groundwater flow meter is sequentially moved in correspondence with each aquifer.
It is characterized by this.

  In other words, because of the problem that it is not possible to measure individual pressure heads in boreholes in multi-layer aquifers, by detecting changes in groundwater flow in each aquifer in boreholes, Is to measure.

In order to measure each pore water pressure (pressure head), pressure measurement is generally used. However, in the present invention, the groundwater flow change in each aquifer is grasped simultaneously with the water level in the borehole. It has a great feature in measuring this.

If the pore water pressure measurement method of the multilayer aquifer according to the present invention,
There is an excellent effect that the pore water pressure (pressure head) of each aquifer can be simultaneously and accurately measured in a multi-layer aquifer without installing a seal layer or a water-impervious layer at one borehole.

It is schematic structure explanatory drawing (the 1) which shows one Example of the pore water pressure measuring method of the multilayer aquifer by this invention. It is schematic structure explanatory drawing (the 2) which shows one Example of the pore water pressure measuring method of the multilayer aquifer by this invention. It is schematic structure explanatory drawing (the 3) which shows one Example of the pore water pressure measuring method of the multilayer aquifer by this invention. It is schematic structure explanatory drawing (the 4) which shows one Example of the pore water pressure measuring method of the multilayer aquifer by this invention. It is schematic structure explanatory drawing (the 5) which shows one Example of the pore water pressure measuring method of the multilayer aquifer by this invention. It is schematic structure explanatory drawing (the 6) which shows one Example of the pore water pressure measuring method of the multilayer aquifer by this invention. It is schematic structure explanatory drawing which shows one Example of a groundwater flow direction meter.

  The present invention will be described below with reference to embodiments shown in the drawings.

FIG. 1 to FIG. 6 are diagrams showing a schematic configuration of a multilayer aquifer 1 according to an embodiment in cross section, and the multilayer aquifer 1 includes a first pressure zone through a hardly permeable layer 2. A second pressurized aquifer 5 is formed through the water layer 4 and the hardly water-permeable layer 3.
A single bored hole 6 is drilled through the ground of the multilayer aquifer 1 through the first and second aquifers 4 and 5. In the present invention, the boring hole 6 may be excavated at one place. This is a feature of the present invention.

After drilling the borehole 6 at one location, the depth positions of the first and second aquifers 4 and 5 in the ground of the multi-layer aquifer 1 are determined at the time of drilling. Measure in advance.

Next, depending on the properties of the ground of the multi-layer aquifer 1 to be excavated, a casing pipe is inserted as necessary to protect the hole wall of the borehole 6 or the borehole 6 is cleaned after excavation, It is necessary to remove the mud film adhering to the surface.
Thereafter, a pore water pressure gauge 7 is disposed in the borehole 6 and groundwater flow meters 8 and 8 are respectively provided at the corresponding positions corresponding to the depth positions of the measured first and second pressured aquifers 5 and 5. Place.

Here, the configuration and type of the pore water pressure gauge 7 are not limited at all. For example, the water pressure change due to the water depth change is measured by a pressure sensor or the like, and converted into an electric signal of DC 4 mA to 20 mA as an example. Then, it is possible to transmit in a two-wire system, and it is possible to embed in the boring hole 6 and measure the pore water pressure in the boring hole 6.

  A so-called electric pore water pressure gauge is a pressure gauge having a structure capable of measuring only the water pressure, and has a configuration in which the water pressure is changed into an electric quantity by a pressure transducer. The required capacity and accuracy are required depending on the expected pore water pressure, and the pressure receiving part has a structure including a filter. As the cord, a cord that can transmit the amount of electricity to the indicator is used, and the indicator that is compatible with the electric pore water pressure meter is used.

Although it is an example of the installation method of the said pore water pressure gauge 7, if it inserts in the boring hole 6 slowly and gently, tightening a rod one after another to the gap water pressure gauge main body, for example, if it reaches the hole bottom or the hole bottom, A method of gently pushing down to a predetermined depth is used.
As understood from FIGS. 2 to 6, the pore water pressure gauge 7 is set at a substantially intermediate position in the depth direction of one drilled borehole 6, but is not limited to this position.

Next, the groundwater flow direction meter 8 is installed in the borehole 6. In the present embodiment, the two groundwater flow direction meters 8 and 8 are installed in the boring hole 6. That is, one is installed at a location corresponding to the first pressurized aquifer 4 and one is installed at a location corresponding to the second pressurized aquifer 5. This is because it is necessary to measure the flow direction of groundwater in each of the confined aquifers 4 and 5.
By the way, the above groundwater flow direction meter 8 can be covered by the use of only one unit.
That is, one groundwater flow direction meter 8 is sequentially moved to the position corresponding to the depth position of the measured first and second pressurized aquifers 5 and 5. If it moves sequentially in this way, there is an advantage that it is not necessary to use only one groundwater flow meter 8 or to prepare a plurality of groundwater flow meters 8.
Here, the configuration and type of the groundwater flow direction meter 8 are not limited at all, but an example thereof is shown in FIG.

  That is, the groundwater flow meter 8 includes a main body 10 having a substantially cylindrical shape having a space 9 therein, and an imaging means housed in the upper part of the main body 10 in the main body 10. 11 and a measurement unit 12 that is provided below the imaging means 11 and measures at least the flow direction of the passing groundwater.

For example, a measuring body 13 that can swing in the horizontal direction extends from the bottom surface of the measuring unit 12 so as to extend in the vertical direction, and a mark serving as a mark for imaging by the imaging means 11 is provided on the top of the measuring body 13. The float 14 provided with is provided.
Accordingly, when the groundwater flows in either direction (method indicated by an arrow), the measurement body 13 swings in that direction in the measurement unit 12. Therefore, the flow direction of groundwater can be measured continuously and over a long period by imaging the state with the imaging means 11.

  In addition, as above-mentioned, in this invention, the kind and structure of the groundwater flow direction meter 8 are not limited at all, and it is necessary to be the groundwater flow direction meter 8 capable of measuring at least the direction of the groundwater flow.

Next, the measurement method according to the present invention will be described.
As can be seen from FIG. 1, in this embodiment, the initial water level in the borehole 6 is GL-1m.

  Further, in FIG. 1, the right side of FIG. 1 will be described by showing in advance the pore water pressure (pressure head) of each layer of the multilayer aquifer 1 in this embodiment. Therefore, the pore water pressure of the first aquifer 4 is GL-2m, and the pore water pressure of the second aquifer 5 is GL-4m.

After installing equipment such as various pore water pressure gauges 7 and groundwater flow direction meters 8 as described above, first, an operation of lowering the water level in the borehole 6 is performed (see FIG. 2).
Although there is no limitation on this operation method, for example, it is conceivable to use a pump to quickly draw up water in the borehole 6 and lower the water level.

For example, after the water level is lowered using a pump or the like, the water level in the borehole 6 is waited for to stabilize, and then the water level in the borehole 6 is recovered. There is no need to perform any work for the recovery, and it will wait for a natural recovery.
And the measurement operation | work mentioned later is performed in progress in this recovery | restoration.

That is, the groundwater flow direction change point of each of the first and second aquifers 4 and 5 is measured by the groundwater flowmeters 8 and 8 installed corresponding to each aquifer, and the inside of the borehole 6 at the time of change is measured. The water level surface position is measured by the pore water pressure gauge 7.
Here, the change of the groundwater flow direction of each first aquifer 4 or second aquifer 5 is, in other words, the flow of groundwater in each first aquifer 4 or second aquifer 5 is stopped. The position of the water level surface in the borehole 6 at this time is measured by the pore water pressure gauge 7.

More specifically, referring to FIG. 2 to FIG. 6, as understood from FIG. 2, the water level was lowered by 7 m from GL in the borehole 6.
Here, as shown in FIG. 2, the initial water level is -1 m from GL, the water level of the first aquifer 4 is GL-2m, and the water level of the second aquifer 5 is GL-4m. Yes. Therefore, when the water level is lowered by 7 m, the direction of the groundwater flow is leftward as shown by the arrow in the first aquifer 4 or the second aquifer 5.

Next, as the water level in the borehole 6 recovers to GL-4 m, as understood from FIG. 3, in the second aquifer 5, both the groundwater levels, that is, the water level in the borehole 6 and the second aquifer. The water level at 5 is in equilibrium, and the direction of the groundwater flow is lost and stops.
This state is measured as the pore water pressure (pressure head) of the second aquifer 5. That is, the water level in the borehole 6 when the groundwater flow stops is measured as GL-4m by the pore water pressure gauge 7.
Furthermore, as shown in FIG. 4, when the water level in the borehole 6 recovers and becomes GL-3m, the flow direction of the groundwater in the second aquifer 5 changes and flows to the right as indicated by the arrows.

Next, as shown in FIG. 5, when the water level in the borehole 6 recovers to GL-2m, both groundwater levels are in an equilibrium state in the first aquifer 4, thereby eliminating the direction of the groundwater flow, That is, the water level in the borehole 6 and the water level of the first aquifer 4 are in an equilibrium state, and the groundwater flow stops.
Thus, when the groundwater flow stops, the water level in the borehole 6 is measured as GL-2m with the pore water pressure gauge 7, and the value is the pore water pressure of the first aquifer 4 (pressure head). It is judged.

Furthermore, as shown in FIG. 7, when the water level in the borehole 6 recovers and becomes GL-1.5 m, the flow direction of the groundwater in the first aquifer 5 flows to the right as indicated by the arrow.
Therefore, in the present invention, it is preferable to repeat each measurement operation at least a plurality of times, preferably three or more times after the water level in the borehole 6 is lowered.
As a result, variations in measurement values and errors can be eliminated, and highly accurate measurement values can be obtained.

DESCRIPTION OF SYMBOLS 1 Multilayer aquifer 2 Hardly permeable layer 3 Difficultly permeable layer 4 1st aquifer 5 5 2nd aquifer 6 Boring hole 7 Pore hydrometer 8 Groundwater flow meter 9 Space part 10 Main body 11 Imaging means 12 Measuring part 13 Measuring object 14 Float

Claims (4)

Drilling a boring hole through the multilayer aquifer through the multilayer aquifer, measuring the depth position of each aquifer in the multilayer aquifer after drilling,
Next, a pore water pressure meter is disposed in the borehole, and a groundwater flow meter is disposed at a corresponding location of each measured aquifer depth position,
After performing the water level lowering operation in the borehole, the groundwater flow direction of each aquifer is changed by the groundwater flow meter installed corresponding to each aquifer during the course of recovery of the water level in the borehole. Measuring the time point, measuring the water level surface position in the borehole at the time of the change by the pore water pressure gauge, and measuring the pore water pressure of each aquifer from the measured value,
A method for measuring pore water pressure in a multilayer aquifer.
Drilling a boring hole through the multilayer aquifer through the multilayer aquifer, measuring the depth position of each aquifer in the multilayer aquifer after drilling,
Next, a pore water pressure meter is disposed in the borehole, and a groundwater flow meter is disposed at a corresponding location of each measured aquifer depth position,
After performing the water level lowering operation in the borehole, the flow of groundwater in each aquifer is measured by the groundwater flow direction meter installed corresponding to each aquifer during the course of recovery of the water level in the borehole. Measuring the time point when the water is stopped, measuring the position of the water level surface in the borehole at the time of the stop using the pore water pressure gauge, and measuring the pore water pressure of each aquifer from the measured value,
Method for measuring pore water pressure in a multilayer aquifer
After performing the water level lowering operation in the boring hole, during the process of recovering the water level in the boring hole, the measurement performed was performed a plurality of times, and the measurement accuracy was improved.
The method for measuring pore water pressure in a multilayer aquifer according to claim 1 or 2, wherein
The groundwater flow meter is a single unit, and the single groundwater flow meter is sequentially moved in correspondence with each aquifer.
The method for measuring pore water pressure in a multilayer aquifer according to claim 1, 2, or 3.

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