Pressure Cells: Types, Working, Principle, & Application

Pressure cells are used to measure the pressure in earth fills and embankments; as well as pressure on the surface of retaining walls, buildings, bridge abutments and tunnel linings. Encardio Rite is the world's leading manufacturer and supplier of six different types of pressure cells that are used in geotechnical monitoring and surveying.
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1. ADIO RITE

Æ EN

Ee oer E CESSE

TYPES, WORKING PRINCIPLE, & APPLICATIONS

2. TABLE OF

CONTENT

WHAT IS A PRESSURE CEL

USES OF PRESSURE CELLS IN
GEOTECHNICAL FIELD

WORKING PRINCIPLE OF
A PRESSURE CELL

TYPES OF PRESSURE CELLS

3. WHAT IS A PRESSURE CELL?

Pressure cells are one of those geotechnical instruments that are designed to
monitor stress or pressure on concrete structures, retaining walls, abutments,
embankments, buildings, tunnel linings, etc.

A pressure cell is a transducer that converts pressure or stress into a readable
electrical output. They are specially designed to measure the total stress in
various construction fields.

Pressure cells are available in different shapes, sizes, and types.

4. USES OF PRESSURE CELL IN GEOTECHNICAL FIELD

The rock/soil formation is completely dependent on the rock/soil type, stress
history, shear, and normal stress levels, boundary and drainage conditions, and
several environmental effects.

The precise assessment of stress and changes that occur in foundation
soil/rock formations is of great importance for safe engineering design.

While constructing the large civil engineering projects like tall buildings, dams,
underground tunnels, etc., measurement of stress plays a vital role.

The types of stress can be categorized as:
Measurement of total stress at a point within a soil mass/foundation

rock/concrete structure.
Measurement of contact stress against the face of a structural element.

5. 2 USES OF PRESSURE CELL IN GEOTECHNICAL FIELD

The vibrating wire pressure cells are much reliable and faster than all the other
types as they are capable of taking readings electrically as the frequency
output is almost immune to external noise.

The cable from the pressure sensor is connected to the readout unit or data
logger and is protected against any possible damage during construction to

6. USES OF PRESSURE CELL IN GEOTECHNICAL FIELD

The applications of pressure cells (stress cells) are as below-

. Pressure cells are designed to monitor radial and tangential stresses in
shotcrete tunnel linings, underground excavations, unlined caverns,
foundations.

. Pressure Cells are used to assess the adequacy of the shotcrete lining.

. They are used to monitor mine backfill.

. To measure the orientation and magnitude of total pressure and stress
distribution within dam embankments and the interface of soil and concrete.

. To determine contact pressure on retaining and diaphragm walls, piers, and

abutments

7. WHAT IS THE WORKING PRINCIPLE OF A PRESSURE CELL?

A pressure sensor converts the stress or applied pressure into measurable
electrical output.

Pressure can be defined as the applied force per unit area that a fluid exerts on
its surroundings. The pressure is given by:

Pressure (P) = Force (F)/Area (A)

The pressure transducers consist of a sensor with a constant area and respond
to the force applied by fluid pressure.

The force applied tends to deflect the diaphragm inside the pressure cell. The
deflection of the diaphragm is calculated and converted into readable
electrical output by the data loggers or readout units.

8. TYPES OF PRESSURE CELLS

Model EPS-30V-Series Earth and Concrete Pressure Cells

The Encardio-Rite earth and concrete pressure cell primarily consist of a
flexible and circular flat capsule constructed from two stainless steel discs.

These stainless steel discs are welded around the periphery and connected to
a specially designed Encardio-rite pressure transducer incorporating the latest
vibrating wire technology.

The vibrating wire technology allows for remote and digital readout. The
pressure cell has inherently high sensitivity and, it is not necessary to produce
a large strain on the area being monitored for the measurement of stress.

9. TYPES OF PRESSURE CELLS

Encardio-Rite offers three types of Model EPS-30V-Series pressure cells:
Model EPS-30V-S

Earth Soil Pressure Cell - Suffix 'S’: for use in soil, earth or rock fills

The Model EPS-30V-S Earth Soil Pressure Cell is 200 mm ® x 7 mm thick. It
consists of two stainless steel diaphragm plates welded around the periphery.

The pressure pad is connected to the vibrating wire pressure sensor through a
6 mm dia x 165 mm long stainless tube. The narrow cavity inside the pressure
pad and the tube is filled with fluid.

10. TYPES OF PRESSURE CELLS

Model EPS-30V-C

Concrete Pressure Cell - Suffix ‘C’: for use in concrete

The Model EPS-30V-C Concrete pressure capsule is similar to EPS-30V-S. For
applications in which the concrete pressure cell is embedded in concrete, a
600 mm long pinch tube is welded to the transducer.

Once the concrete is cured, due to cooling the shrinkage of capsule is created
which creates a gap between the concrete and cell which prevents the
transmission of pressure on the cell.

Thus to fill the gap, a pinch tube is squeezed to push the fluid to inflate the cell
and develop a positive pressure on it.

11. 4

TYPES OF PRESSURE CELLS

Model EPS-30V-I

Soil and Rock-Concrete Interface Pressure Cell - Suffix ‘I’: for use at concrete

and soil interface
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The Model EPS-30V-| Soil and Rock-Concrete Interface Pressure Cell is similar
to the above except that it is 200 mm x 10 mm thick and the diaphragm on

12. TYPES OF PRESSURE CELLS

> Model EPS-30V-J Jack Out Pressure Cell

The total stress measurement in the soil can be categorized as follows:

. Measurement within a soil mass.
. Measurement at the face of a structural element.

Encardio-Rite Jack-Out Pressure Cell falls in the latter category. The name of

the cell is derived from the use of a hydraulic jack during installation by
activating it to keep the cell in position while the concrete is poured in.

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13. TYPES OF PRESSURE CELLS

Encardio-Rite Model EPS-30V-J-® Jack-Out Pressure Cell is used for monitoring
changes in stress base slabs and diaphragm/slurry walls etc. It is extensively
used:

Where concrete is cast directly against soil, i.e. cast in place structures.
As a safety measure to monitor the earth pressure in excess of designed limits.
For verification of design assumptions and to provide data and information for
safer and more economical future designs

The Model EPS-30V-J Jack-Out Pressure Cell is designed to measure the total
stress i.e. the effective stress due to the soil together with the pore water

pressure in the voids between soil grains.

It is suitable for measuring static or slowly varying stresses only.

14. TYPES OF PRESSURE CELLS

Construction of Model EPS-30V-J Jack Out Pressure Cell

The Jackout Pressure cell is 14 mm thick and has a diameter of either 200 mm
or 125 mm. It is constructed from two stainless steel plates welded together
around the periphery so as to leave a narrow space between them

15. TYPES OF PRESSURE CELLS

This space is completely filled with de-aired fluid and connected hydraulically
to a pressure sensor.

The sensor has an all welded construction such that space confining the
hydraulic fluid is entirely metal, not requiring 'O' rings that tend to trap air and
reduce cell stiffness.

The hydraulic fluid is de-aired which materially improves fluid stiffness and
performance of cell.

The pressure transducer is made of stainless steel construction with size
42 mm ® x 176 mm long.

It incorporates the latest vibrating wire technology and has an inherently high
sensitivity.

16. TYPES OF PRESSURE CELLS

The transducer converts the fluid pressure into an electrical signal in the form
of frequency, which can be accurately measured by model EDI-51V vibrating
wire readout unit or any other conventional vibrating wire readout unit.

The signal can also be transmitted over long distances to a remote automatic
data acquisition system like Encardio-Rite Model EDAS-10.

17. TYPES OF PRESSURE CELLS

Model ESC-30V Shotcrete-Concrete Stress Cell

The Model ESC-30V is used to monitor the radial and tangential stresses in the
shotcrete of tunnels, particularly where the New Austrian Tunnelling Method
and underground works are being implemented.

Measurement of radial and tangential stresses within shotcrete lining is a vital
feature of this type of stress cell.

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18. TYPES OF PRESSURE CELLS

The stress cell has a rectangular pressure pad which is constructed with two
stainless steel plates, welded around the periphery.

The pressure pad and the electron beam welded vibrating wire pressure
sensor are connected together by a 6 mm ® x 165 mm long stainless steel
tube.

The cavity inside the pressure sensor and the pressure pad is filled with
de-aired fluid

19. TYPES OF PRESSURE CELLS

Construction of Model ESC-30V Shotcrete-Concrete Stress Cell

Increase in stress in the concrete causes a vibrating wire pressure cell and is
converted to an electrical signal which is transmitted as a frequency signal to
read out the unit

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

Any deflection of the diaphragm changes the tension in the wire, thus affecting
the resonant frequency of the vibrating wire. The resonant frequency with
which the wire vibrates can be accurately measured by the vibrating wire
readout unit.

20. 7

THANK YOU

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