1. Q. What is Piezometer? Describes the various types of
piezometers and their uses.
Piezometer is an instrument to measure pore water pressure. it is one of the
simplest forms of manometers which consists of a glass tube, whose one
end is connected to a point where the pressure is to be measured and the
other end is open to atmosphere. It can be used for measuring moderate
pressures of liquids. The pressure at any point in the liquid is indicated by
the height of the liquid in the tube above that point.
A piezometer is designed to measure static pressures. It can have various
functioning principles, depending on where you want to take the
measurement. The most famous one is the Casagrande’s piezometer, widely
used to measure pore pressure in granular soils. As shown in fig.1.
Figure 1 Piezometer inside a pipe
2. There are the different types of piezometer.
1. OPEN STANDPIPES
The simplest instrument for measuring pore water pressures in the ground
is an open standpipe. This is a small (usually 19mm) diameter plastic pipe
with a porous section at the bottom. The pipe is installed inside a borehole
and the porous section is positioned at the depth where the pore water
pressure is to be measured. The annulus between the porous filter and the
borehole is filled with sand, the top and bottom surfaces of the sand are
sealed with bentonite and the rest of the borehole is filled with a
cement/bentonite grout.
The pressure of the ground water pushes water into and up the standpipe
until the level of water inside the standpipe (h) is equivalent to the pore water
pressure in the ground at the elevation of the porous filter. As shown in fig.2.
Figure 2 Open standpipe
3. 2. ELECTRIC PIEZOMETERS
Electric piezometers consist of a deflecting diaphragm and a porous filter
separated by a small reservoir of water. Deflections of the diaphragm are
detected using a vibrating wire or a strain gauge and are converted to an
equivalent pressure using a suitable calibration.
The piezometer is inserted into a borehole and the annulus between the
porous filter and the borehole is filled with either sand or cement/bentonite
grout. Water from the ground forces its way into the reservoir and causes the
diaphragm to deflect until the pressure inside the reservoir is the same as
the pore water pressure in the ground at the elevation of the porous filter. As
shown in fig.3.
Figure 3 Electric piezometers
4. 3. HYDRAULIC PIEZOMETERS
Hydraulic piezometers consist of a porous filter enclosing a reservoir of
water, which is separated from a pressure gauge by flexible, water filled
tubes. The tubes are used to circulate water through the system, removing
air and ensuring that the reservoir remains full of water. Geotechnical
Observations’ flushable piezometer is a hydraulic piezometer that can
measure positive and negative pore water pressures. As shown in fig.4.
Other types are,
a. Vibrating Wire piezometers: It is the piezometer which is the mostly
commonly deployed type of piezometer. Suitable for the most
applications. It can be installed in a borehole, embedded in fill or
suspended in a standpipe.
Figure 4 Hydraulic piezometers
5. b. Pneumatic piezometers: It is the piezometer which operates by gas
pressure. It can be installed in a borehole, embedded in fill pr
suspended in a large diameter standpipe. Reading are obtained with a
pneumatic indicator.
c. Titanium piezometer: It is the piezometer which is a 4-20 MA device
that is compatible with industrial data loggers. It is generally used for
drawdown tests.
The major uses of piezometer are.
a. It is mainly used for exploring and measuring water pressure/water
levels below the earth’s surface.
b. Piezometers are commonly used in special wells.
c. Pore pressure measurement in soils and rocks.
d. Fluid pressures in hydro-fracture and pump tests.
e. Understand initial site conditions.
f. Determine safe rates for placement of fill.
g. Predict slope stability.
h. Evaluate the effectiveness of drainage schemes
i. Check the performance of containment systems.
j. Monitor performance of clay core & Monitor seepage.
THANK YOU!!!
Name: Milan Kumar Rai
Roll No.: 17
