ISO 18674-4:2020 地盤調査とテスト—フィールド計装による地盤モニタリング—パート4：間隙水圧の測定：ピエゾメータ | ページ 5

3.1

piezometer

field instrument system for measuring pore water pressure (3.2) or piezometric level (3.4) where the measuring point (3.15) is confined within the ground or geotechnical fill so that the measurement responds to the fluid pressure around the measuring zone/point and not to fluid pressures at other elevations

Note 1 to entry: The system consists of a sealed reservoir (3.1.2) filled with fluid, a filter (3.1.3) and a measuring device (3.1.7) .

Note 2 to entry: The system is either an open piezometer system (3.6) or a closed piezometer system (3.7) .

3.1.1

intake zone

zone confined by seals (3.1.6) , between which water in the ground can flow to the measuring device, thus defining the measuring point (3.15)

Note 1 to entry: See Figure 1.

Note 2 to entry: It is assumed that a hydrostatic pore water pressure (3.2) distribution is established along the intake zone.

Note 3 to entry: The constant of proportionality between flow into or out of a piezometer (3.1) and the change of pore water pressure is called the intake factor F.

3.1.2

reservoir

space between the ground and the measuring device (3.1.7) , occupied by a fluid, which allows the pore water pressure (3.2) to act on the sensing element of the measuring device

Note 1 to entry: The pores within the filter (3.1.3) are an integral part of the reservoir.

Note 2 to entry: In open piezometer systems (3.6) , the water-filled part of the standpipe is part of the reservoir.

3.1.3

filter

permeable section of a piezometer (3.1) defining the intake zone (3.1.1) , which allows water to enter and at the same time restricts soil particles entering the standpipe or measuring device (3.1.7)

Note 1 to entry: The filter can be a combination of elements, such as a sand pocket, a perforated pipe, a geotextile sleeve, a filter tip (3.1.4) and grout backfill in specific cases.

3.1.4

filter tip

filter (3.1.3) element which is a common part of a closed piezometer system (3.7)

Note 1 to entry: Filter tips are formed of a material with purpose-designed pore diameters, i.e. HAE filter (3.1.4.1) or LAE filter (3.1.4.2) .

3.1.4.1

high air entry filter

HAE filter

filter tip (3.1.4) with comparatively small pores giving a higher resistance to the passage of air than to the passage of water

Note 1 to entry: Commonly, high air entry filter tips have pore diameters of between 1 μm and 3 μm.

Note 2 to entry: HAE filter tips are used when it is intended to keep gas out of the measuring device (3.1.7) .

Note 3 to entry: In unsaturated soil or when negative pore water pressures (3.2) are to be measured (i.e. suction; see Annex F), the pressure of the gaseous phase is always higher than that of the pore water. The required pore diameter of the HAE filter tip depends on the difference between the pore air pressure and the pore water pressure.

3.1.4.2

low air entry filter

LAE filter

filter tip (3.1.4) with comparatively large pores giving a lower resistance to the passage of air readily allowing the passage of both air and water

Note 1 to entry: Commonly, low air entry filter tips have pore diameters of between 20 μm and 50 μm.

3.1.5

filter pack

permeable material, placed around a slotted section of an open piezometer (3.1) or around the filter tip (3.1.4) , allowing water to reach the measuring device (3.1.7)

3.1.6

seal

layer in a borehole, made with a material that has a permeability suitable for hydraulical separation of two aquifers (3.10)

Note 1 to entry: Seals are generally used to confine an intake zone (3.1.1) .

3.1.7

measuring device

part of the piezometer (3.1) system used to measure the piezometric level (3.4) in an open system (3.6) or the pore water pressure (3.2) in a closed system (3.7)

Note 1 to entry: For an open piezometer system (3.6) , the measuring device is commonly a water level meter (3.1.7.1) for manual measurements or a pressure transducer for automatic measurements.

Note 2 to entry: For a closed piezometer system (3.7) , the measuring device is typically a diaphragm pressure transducer (see 7b in Figure 1 b)). The diaphragm separates a reservoir (3.1.2) and an inner chamber in the transducer. The deflection of the diaphragm is a function of the pore water pressure (3.2) (see Figure 3).

Note 3 to entry: For closed piezometer systems, the measuring device is often synonymously termed a piezometer in a narrow sense.

3.1.7.1

water level meter

measuring device with a marked length measuring tape and a tip that activates a signal (light, sound) when it comes into contact with water

Note 1 to entry: A water level meter is commonly used for manual measurements in open systems (3.6) or during the installation procedure of piezometers (3.1) .

3.1.7.2

electric piezometer

piezometer (3.1) where the measuring device (3.1.7) has a diaphragm and the deflection of the diaphragm due to pore water pressure (3.2) is measured by an electric sensor

Note 1 to entry: Electric piezometers are commonly based on strain gauge, piezo-electric, vibrating wire or capacitive sensors. Data acquisition devices exist which accommodate all types of electric piezometers.

Note 2 to entry: See Figure 3.

3.1.7.3

fibre optic piezometer

piezometer (3.1) where the pressure measuring device (3.1.7) has a diaphragm and the deflection of the diaphragm is measured by an optical sensor

Note 1 to entry: Fibre optic piezometers do not require electrical connection between read-out unit and sensor.

Note 2 to entry: Fibre optic piezometers require a dedicated read-out unit.

3.1.7.4

pneumatic piezometer

piezometer (3.1) where the pressure measuring device (3.1.7) has a valve which is opened pneumatically by a gas pressure, which is applied from the outside via gas-filled tubes and closed by the pore water pressure (3.2)

Note 1 to entry: See Figure 4.

3.2

pore water pressure

u

pressure of the water in the voids of the ground or a fill, relative to the atmospheric pressure

Note 1 to entry: The pore water pressure is the difference between the total stress and the effective stress in saturated ground (see References [6] and [7]).

Note 2 to entry: For rocks, the associated term is joint water pressure.

Note 3 to entry: The state of soil or fill where the pores are completely filled with water is referred to as “saturated”.

Note 4 to entry: Pore water pressure measurements can yield positive or negative values (see Reference [8] and Annex F). Instruments that directly measure negative pore pressures are sometimes termed ‘tensiometers’, but are not within the scope of this document (see ISO 11276).

Note 5 to entry: Measurements of the pore water pressure can be affected by changes of the atmospheric pressure (see 5.4.1 and Annex A).

3.3

pressure head

ψ

ratio u/γ_w of the pore water pressure u (3.2) and the specific weight of water γ_w, above a point

Note 1 to entry: For an open piezometer system (3.6) , it is proportional to the elevation difference between the piezometric level (3.4) and the level of the measuring point (3.15) (see Figure 1).

3.4

piezometric level

z_w

elevation to which water will rise in an open standpipe piezometer (3.6.1) and at which the pressure of the water in the ground is equal to that of the ambient atmosphere

Note 1 to entry: The piezometric level z_w is the sum of the geometric elevation z and the pressure head ψ (3.3) : z_w = z + u/γ_w.

Note 2 to entry: See Figure 1.

3.5

groundwater table

water table

elevation at which pore water pressure u (3.2) is zero

Note 1 to entry: See Figure 1.

Note 2 to entry: An equivalent term is phreatic surface.

Note 3 to entry: The groundwater level is the level of the groundwater table at a geographical coordinate.

3.6

open system

open piezometer system

field instrument system in which the fluid is in direct contact with the atmosphere and the piezometric level (3.4) at the measuring point (3.15) is measured

3.6.1

open standpipe piezometer

open piezometer system (3.6) , consisting of a pipe (installed in the ground) which, at its upper end, is open to the atmosphere and with a perforated section, located in the intake zone (3.1.1)

Note 1 to entry: See Figure 1 a).

Note 2 to entry: Typical inner diameters of the pipe are from 19 mm to 60 mm.

3.6.2

Casagrande piezometer

open standpipe piezometer (3.6.1) with one or two comparatively small inner diameter pipes and a porous filter tip (3.1.4) at the measuring point (3.15)

Note 1 to entry: See 5.2.2.4, Figure 2 and Reference [9].

3.6.3

monitoring well

open standpipe piezometer (3.6.1) with a large inner diameter of the pipe (typically ≥100 mm)

Note 1 to entry: A monitoring well can be used as standpipe piezometer (3.1) , if the response time (3.9) is satisfactory (see Annex D).

Note 2 to entry: A monitoring well is often used for taking samples of the groundwater or for performing pumping tests.

3.6.4

observation well

open pipe within a borehole ここで, the intake zone (3.1.1) is unconfined

Note 1 to entry: Observation wells are often incorrectly termed open standpipe piezometers (3.6.1) . Observation wells do not classify as piezometers (3.1) as they do not have seals (3.1.6) .

Note 2 to entry: See 5.2.2.3.2.

3.7

closed system

closed piezometer system

measuring system in which the reservoir (3.1.2) is not in direct contact with the atmosphere and in which the pressure in the fluid is measured by a pressure measuring device (3.1.7)

Note 1 to entry: See Figure 1 b).

Note 2 to entry: Examples for pressure measuring devices, used in closed systems, are electric transducers, fibre optic transducers and pressure valves.

3.7.1

diaphragm piezometer

closed system (3.7) with a filter tip (3.1.4) , a small reservoir (3.1.2) and diaphragm which separates the pore water from the measuring system

Note 1 to entry: The deflection of the diaphragm is measured and the signal is transported through a cable to an accessible location.

Note 2 to entry: Possible diaphragm piezometers are electric piezometers (3.1.7.2) or fibre optic piezometers (3.1.7.3) .

Note 3 to entry: The pressure is measured adjacent to the filter tip.

3.7.2

closed hydraulic twin-tube piezometer

closed system (3.7) with a porous ceramic filter tip (3.1.4) located within an intake zone (3.1.1) and connected to a remote location via twin fluid filled tubes

Note 1 to entry: The pressure measurement takes place at the remote location and not at the filter tip. The measurements need to be adjusted for elevation differences between the filter tip and the remote location.

3.7.3

probe piezometer

closed system (3.7) where a moveable measuring device (3.1.7) is inserted into a pipe which is equipped with one or more measuring ports, each located at an intake zone (3.1.1)

3.8

multi-level piezometer

system with several measuring points (3.15) permanently installed at different elevations in the ground ここで, each measuring point has its own intake zone (3.1.1)

3.9

hydrodynamic time lag

response time

time span between a change of the pore water pressure (3.2) in the ground and the associated change in the measurement

Note 1 to entry: The time lag depends primarily on the type and dimensions of the piezometer (3.1) (essentially the size of the reservoir (3.1.2) ), the permeability of the ground and the installation procedure (see Annex D).

Note 2 to entry: The term “slow response time” of the piezometer is synonymous with a long hydrodynamic time lag.

3.10

aquifer

body of permeable rock or soil mass suitable for containing and transmitting groundwater

3.11

unconfined aquifer

aquifer (3.10) in which the groundwater surface forms the upper boundary

3.12

confined aquifer

aquifer (3.10) which is bounded above and below by aquicludes (3.14)

3.13

confining layer

aquitard

a low permeability layer of rock or soil that restricts groundwater flow and seperates aquifers (3.10)

3.14

aquiclude

body of soil or rock with extremely low transmissivity, which effectively prevents the flow of water through the ground

3.15

measuring point

point in the ground where the pore water pressure (3.2) is referenced to