Piezometers: Types, Functions & How It Works?

Piezometers are used to measure pore water pressure (Piezometric level) in the ground. The piezometer, also known as pore pressure meter, is used to measure pore water pressure in the soil, earth/rock fills, foundations and concrete structures. It provides significant quantitative data on the magnitude and distribution of pore pressure and its variations with time. It also helps in evaluating the pattern of seepage, zones of potential piping and the effectiveness of seepage control measures undertaken.

Proper evaluation of pore pressure helps in monitoring the behaviour after construction and indicates potentially dangerous conditions that may adversely affect the stability of the structure, its foundation and appurtenant. It also provides basic data for design improvement that will promote safer and more economical design and construction.

1. RPEAQUNERER 5:

TYPES, FUNCTIONS, & HOW IT WORKS?

2. WHAT IS A PIEZOMETER?
TYPES OF PIEZOMETERS
VIBRATING WIRE PIEZOMETERS
WHAT IS PIEZOMETRIC LEVEL?

TABLE OF

CONTENT

3. WHAT IS A PIEZOMETER

» The piezometer or pore pressure meter is used to measure pore water
pressure in the soil, earth fills, foundations and concrete structures.

» It provides significant quantitative data on the magnitude and
distribution of pore pressure and its variations with time

> It also helps in evaluating the pattern of seepage, zones of potential
piping and the effectiveness of seepage control measures undertaken.

> It also provides basic data for design improvement that will promote
safer and more economical design and construction

4. TYPES OF PIEZOMETERS

> Open Standpipe Piezometers

Itis a plastic pipe, with a small diameter (up to 20mm) and a porous section at
the bottom. This pipe is installed inside a borehole while placing the porous
section at the bottom where the piezometric level is to be measured.

The annulus between the porous filter and the borehole has sand in it, sealed
from both the sides using bentonite and, the rest of the borehole is filled with
cement mortar.

The groundwater pressure pushes the water into the standpipe until the level
of water inside the standpipe (h) is equal to the piezometric level (pore water
pressure) in the ground at the elevation of the porous filter.

5. TYPES OF PIEZOMETERS

» Electric Piezometers

Electric piezometers comprise of a deflecting diaphragm and a porous filter
divided by a small reservoir of water. Vibrating wire or a strain gauge is used to
calculate the deflections of the diaphragm. The calculated results are then
converted to an equivalent pressure using a proper calibration

The further procedure is similar to Open Standpipe Piezometers

> Pneumatic Piezometers

The next type of piezometer is the pneumatic piezometer which is operated by
gas pressure. It can be placed in a borehole, fills, or in a large diameter
standpipe. The readings are then calculated with a pneumatic
indicator.calculated results are then converted to an equivalent pressure using
a proper calibration.

6. TYPES OF PIEZOMETERS

> Hydraulic Piezometers

Hydraulic piezometers consist of a porous filter containing a reservoir of
water, separated from a pressure gauge via resilient and water-filled tubes

These tubes circulate water through the system to remove air and ensure
that the reservoir remains filled with water.

The piezometer measures overall hydraulic pressure from which pore
pressure can be calculated. The further procedure is similar to Open
Standpipe Piezometers.

7. VIBRATING WIRE PIEZOMETERS

The Vibrating Wire Piezometers measure the pore water pressure in fully or
partially saturated soil and rock. A vibrating wire piezometer basically consists of
+ Asensitive stainless steel diaphragm
+ A magnetic, high tensile strength stretched wire, one end of which is
anchored and the other end is fixed to a diaphragm
Ceramic low air filter

Thermistor for temperature readings

Glass to metal seal with four terminals for cable connection

Stainless steel body with resistance to rusting or corrosion against several
kinds of dissolved impurities found in water under field conditions.

Glass to metal seal
4-core cable Cable gland

Fiter

Vibrating wire — Magneticcoll — Thermistor

Stainless steel Cable joint
housing housing

8. WHAT IS PIEZOMETRIC LEVEL

The pore water pressure/Piezometric Level is the pressure experienced
by water contained in pores of earth materials or concrete structures

The study of pore pressure has the following main purposes:

+ Effect of water in pores of soil or rock is to reduce load
bearing capacity of soil or rock. The effect is more
pronounced with higher pore water pressure leading
eventually in some cases to total failure of load-bearing
capacity of the soil
To determine the level and flow pattern of groundwater
To determine the flow pattern of water in earth/rock fill,
concrete dams, and their foundations.

To delineate the phreatic line.

9. HOW DOES A VIBRATING WIRE PIEZOMETER WORK?

The vibrating wire piezometer basically consists of a magnetic, high tensile
strength stretched wire, one end of which is anchored and the other end fixed to a
diaphragm that deflects in some proportion to applied pressure.

Any change in pressure deflects the diaphragm proportionally and this, in turn,
affects the tension in the stretched wire. Thus any change in pore pressure directly

affects the tension in the wire

The wire is plucked by a coil magnet. Proportionate to the tension in the wire, it
resonates at a frequency f, which can be determined as follows:

f = {log/p] 1/2 21 Hz

Where o = tension of the wire
g = gravitational constant

p = density of wire

| = length of wire

10. VIBRATING WIRE PIEZOMETER ENCARDIO-RITE’S MODELS

> Model EPP-30V/Electron Beam Welded Heavy-Duty
Vibrating Piezometer

The vibrating wire and coil magnet assembly are enclosed in a stainless steel body
which is electron beam welded to the diaphragm

This result in a vacuum of around 1/1000 Torr inside the sensor making it immune
to the effect of any ingress of water and other corrosive materials that may be
present in the water

As piezometer is of stainless steel construction, it is not affected by normal
chemical corrosion at locations in which it is used

11. VIBRATING WIRE PIEZOMETER ENCARDIO-RITE’S MODELS

Each sensor has a built-in thermistor for temperature measurement and a surge
arrester for protection from lightning. A glass to metal seal solder pin connector is
provided for an easy cable connection.

These piezometers are suitable for mounting at different levels in a borehole using
the grouting technique.

12. VIBRATING WIRE PIEZOMETER ENCARDIO-RITE’S MODELS

> Encardio-Rite Model EPP-40V Vibrating Slim Wire Piezometer

The EPP-40V is a vibrating wire piezometer specifically designed for pore water
pressure measurement in small diameter boreholes and standpipes. It is made of
stainless steel with a built-in thermistor for temperature measurement and surge
arrester for protection from lightning

A glass to metal solder pin connector is provided for an easy cable connection. The
sensor is hermetically sealed with a vacuum of around 0.001 Torr inside it

13. VIBRATING WIRE PIEZOMETER ENCARDIO-RITE’S MODELS

> Encardio-rite model EPP-60V Vibrating Wire Low-Pressure
Piezometer

EPP-60V low-pressure sensor is specially designed to measure low
water pressure. The basic pressure sensor, in a diameter of 30 mm, is

conveniently designed to measure water level, and water pressure in boreholes.

The pressure sensor is used for applications in which maximum hydrostatic head
(height of water level above piezometer location) is less than 7 m over the sensor

diaphragm.

14. VIBRATING WIRE PIEZOMETER ENCARDIO-RITE’S MODELS

» Encardio-Rite's Model EPU-20V Vibrating Wire Uplift
Pressure System

EPU-20V is a vibrating wire uplift pressure measurement system that uses a
vibrating wire pressure sensor. It is designed for monitoring uplift pressure of
water in the foundation of dams and concrete structures

The sensor is similar to EPP-30V, except that instead of a filter, a 25 mm BSP
adaptor is provided for the connection of a pipe. A perforated/non-perforated
pipe is inserted in the borehole, on top of which the EPU-20V is mounted through
valves and fittings.

15. HOW TO IN: L PIEZOMETER

> In Borehole/Foundation

Installation of piezometer in a borehole is done with a fully grouted method
Installing multiple piezometers in a borehole using the traditional method, which
involves placement of sand pockets surrounding the piezometers, bentonite seals
and grout columns to separate piezometers at different levels, is slow and complex

In Soft Soil

For installation in soft soils the Encardio rite model EPP-50V push-in piezometer is
recommended. It does not require any elaborate grout sealing below and above
the piezometer as required for other piezometer models.

The EPP-50V has a hard conical tip that allows the piezometer to be pushed into
the required depth from the ground surface or the base of a drilled borehole

16. > In Earth & Rock Fill Dam

In an earth and rock fill dam, a number of piezometers and maybe other sensors
are installed at selected elevations at different cross-sections, as shown in the
figure below:

Soll Pressure
Pore Pressure
Under ground settlement it

Seepage measurement

17. HOW TO IN: L PIEZOMETER

» In Concrete Dam

As access galleries are available in concrete dams, the cable from the sensors is
first routed to the gallery. These cables may be terminated in junction boxes inside
the gallery

The data from the various sensors can then be taken or logged from the junction
boxes with the help of a readout unit or data logger.

Alternatively, if required, the signals from the junction boxes may be carried
through multicore cables to any observation room outside the dam structure.

18. APPLICATIONS & LIMITATIONS OF PIEZEM

> Applications

Construction control, stability investigation and monitoring of earth dams,
embankments, foundations, shallow underground works and surface excavations.
Uplift and pore pressure gradients in foundations, embankments, abutments and fills.
The hydrological investigation, groundwater pressure study and

water supply operations.

Pore pressure studies in relation to waste and environmental applications
Monitoring of pore pressure for soil improvement & stability and for slope stability
Reclamation of land in high population density areas in coastal regions for building
highways, multi-storied structures, port trusts or recreational facilities

In coastal areas, it is necessary to determine and implement a strategy to overcome
salinity problems and to increase community understanding and involvement in
finding and implementing a solution.

19. APPLICATIONS & LIMITATIONS OF PIEZEME

> Limitations

+ Use of sensors in saline water is one of the most difficult applications from the point
of view of corrosion. Great care should be taken for corrosion protection in case a
piezometer is used for such applications. This is a tricky application and precaution
must be taken to protect both the body and the diaphragm of the sensor.

It cannot measure the pressure of the gas or vacuum. A piezometer is ideal to
measure only the liquid pressure.

20. THANK YOU