Extensometer Types, How It Works, Applications by Encardio-rite

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EXTENSOMETERS
Types, How it Works Applications
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INTRODUCTION
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WHAT IS AN EXTENSOMETER?
TABLE OF CONTENT
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HOW DOES AN EXTENSOMETER WORK?
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USES OF EXTENSOMETER IN THE GEOTECHNICAL FIELD
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WHAT ARE THE TYPES OF EXTENSOMETERS?
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INTRODUCTION
Extensometers or extension-meters are extensively
used to measure the change in the length of an
object. They are designed for strain
measurements or to carry out tensile tests.
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WHAT IS AN EXTENSOMETER?
An extensometer is a high precision instrument
specially designed for geologists or civil
engineers to measure the elongation of a material
under stress. It can also determine yield
strength, tensile strength, yield point
elongation, strain-hardening exponent, and
strain ratio.
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HOW DOES AN EXTENSOMETER WORK?
The working principle of extension-meters depends
on its type as well as the application
area. Encardio-Rite deals with a wide range of
extensometers, including magnetic, electrical,
mechanical, and soil extensometers. Magnetic
Extensometer The magnetic extensometer system is
designed to measure settlement or heave and
lateral or horizontal ground movement of the soft
ground under the influence of loading or
unloading due to the construction of embankments,
fills, buildings, and structures.
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HOW DOES AN EXTENSOMETER WORK?
Electrical Extensometer The electrical borehole
extensometer incorporates a vibrating wire
transducer for measurement of displacement. A
groutable reinforced bar anchor (1) is attached
to fibreglass (2.a) or AISI 410 stainless steel
(2.b) connecting rods of appropriate length. The
connecting rods are enclosed inside heavy-duty
protective tubing to allow for free
movement. The displacement sensor is coupled to
the connecting rod using link plate and lock nut.
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HOW DOES AN EXTENSOMETER WORK?
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HOW DOES AN EXTENSOMETER WORK?
Mechanical Extensometer The borehole
extensometer measures the extension
(displacement) which takes place with time in a
borehole or several boring holes in a rock
mass. The anchor or anchors are set in the same
borehole or different boreholes drilled ad-
jacent to the first borehole. They help to
accurately measure the distance between the
various anchors with re- spect to the reference
plate and monitor their relative displacement
with time.
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HOW DOES AN EXTENSOMETER WORK?
Soil Extensometer The soil extensometer uses a
vibrating wire sensor for monitoring
displacement. The system consists of a sensor
assembly with flanges that are mounted with adap-
tors, adjustment unit, sockets and extension
rods between two anchors to monitor the
horizontal movement of surrounding
soil. Movement of relative position between two
anchor channels at the ends of the soil
extensometer is representative of the mass
movement.
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USES OF EXTENSOMETER IN THE GEOTECHNICAL FIELD

• To determine how the roof or wall of mine,
  underground cavity or tunnel behaves during
  excavation operation to study the effectiveness
  of the support system.
• To predict potential roof or wall fall before it
  occurs. Roof or wall fall in an under ground
  cavity is almost invariably preceded by
  measurable sag as the strata open up, and the
  movement usually occurs at an increasing rate as
  fall conditions are ap proached. Unsuspected
  roof and wall fall conditions are approached that
  may result in serious accidents.
• To measure and monitor the movement in a slope or
  foundation due to the excavation of underground
  cavities or due to the construction of a heavy
  structure like concrete, rock fill, masonry or
  earth dam over the foundation.
• To measure horizontal and vertical movement in
  foundations and embankments.
• To measure the movement of natural and cut
  slopes, quarry and mining excavations.

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USES OF EXTENSOMETER IN THE GEOTECHNICAL FIELD

• To calculate the displacement of retaining walls,
  piers abutments.
• To measure the displacement around tunnels
  underground cavities.
• They are used for highly accurate measurements of
  relative deformations of multiple segments along
  the entire pile length.

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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EDS-63U-D Mechanical Borehole Extensometer
System The Encardio-Rite Model EDS-63U-D
mechanical borehole extensometer is ideally
suited for upward, downward or inclined
boreholes. Together with anchor bolt load cell
and tape extensometer, it is essential equipment
for investigation and monitoring of foundations,
slopes embankments and for studying the
behaviour of rock around underground cavities,
tunnels and mines.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
The measurement with Model EDS-63U-D borehole
extensometer is economical, very reliable and is
preferred at locations where access to the mouth
of the borehole is easily available The Model
EDS-63U-D borehole extensometer with up to three
positions can be in- stalled in a 3 f NX (76 mm
f) borehole with up to six positions, it can be
installed in a 100 mm f borehole. Groutable
anchor is ideally suited when it is not possible
to install expandable an- chors at locations
where the rock formation is soft.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EDS-64U-D Mechanical Borehole Extensometer
System The Encardio-Rite Model EDS-64U-D single
position mechanical borehole extensom- eter is
suitable for 50 mm upward, downward or inclined
boreholes. It is a precision mechanical
instrument designed to measure the deformation of
rock mass and adjacent or surrounding soil.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EDS-70V/EDS-70P Electrical Borehole
Extensometer System The Encardio-rite Model
EDS-70V multi-point borehole extensometer is a
precision instrument designed to help civil
engineers and geologists in the measurement of
deformation of rock mass adjacent or
surrounding soil. The borehole extensometer is
an important instrument especially in the
investiga- tion of underground cavities
landslides.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
The Model EDS-70V borehole extensometer
incorporates a vibrating wire transducer for
measurement of displacement. EDS-70V can be
ordered from the factory for monitoring
settlement at up to six depths. It is suitable
for a 3 ? (76 mm) borehole for up to 13 points
4 ? (102 mm) borehole for 46 points. Model
EDS-70M version of this borehole extensometer is
available for taking the reading with a
mechanical dial gauge and is supplied without the
vibrating wire sen- sors. Model EDE-VXX
vibrating wire linear displacement transducer
incorporates a vibrat- ing wire sensor having a
stroke of 50 mm (EDE-V05), 100 mm (EDE-V10) or
150 mm (EDE-V15).
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EDS-71V/EDS-71P Electrical Borehole
Extensometer System The Encardio-Rite Model
EDS-71V electrical borehole extensometer is a
precision in- strument designed to help civil
engineers and geologists in the measurement of
de- formation of rock mass and adjacent or
surrounding soil.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EDS-91 Magnetic Extensometer System The
Encardio-rite Model EDS-91V/H magnetic
extensometer is used to measure ver- tical
settlement or lateral movement depending on the
application. Settlement or heave at various
levels within a soil mass may be assessed by
moni- toring location of magnetic targets which
have been positioned over a near-vertical access
tube.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
For monitoring settlement only, regular access
tubing is used. For monitoring lateral
displacement along with the settlement,
inclinometer casing with telescopic coupling is
used. For vertical installation in an earth
fill, 3 m long tubes are connected, one by one,
with telescopic couplings to keep pace with the
fill operation. For horizontal installations,
similar telescopic access tubes are laid at the
base of the trench, with magnet plates embedded
in the trench floor. The probe, 22 mm F x 150 mm
long has a reed switch encapsulated inside it in
sili- con rubber for protection against shock,
corrosion and ingress of water. The
moisture-resistant electronics and standard 9 V
PP-3 size battery are housed in a hub on the
cable reel can be easily removed to replace the
battery or check the electronics without
disassembling the entire cable reel.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EDS-92 Soil Extensometer The Encardio-rite
model EDS-92 extensometer is used for monitoring
displacement between two surfaces that may shift
with respect to each other with time. The soil
extensometer finds major application in the
measurement of lateral strains and settlement in
or beneath earth/rock fill embankments.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
The displacement of retaining walls, bridge piers
and abutments can also be moni- tored by the
soil extensometer. It also measures displacement
across construction joints in concrete, and
across joints/faults in the rock. The
extensometers are usually installed in
approximately 500 mm wide x 600 mm deep trenches.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EMA-11 Measuring Anchor The Encardio-Rite
Model EMA-11 measuring anchor (rock bolt
extensometer), is a combination of rock bolt and
an extensometer. EMA-11 Measuring anchor is used
to determine the load exerted on rock bolts. The
principal function of measuring anchor is to
determine the depth where force is exerted on
the bolt due to loosening effects of rock.
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WHAT ARE THE TYPES OF EXTENSOMETERS?
Model EMA-11 measuring anchor has a breaking
force of up to 250 kN and the length offered
ranges from 3 m to 6 m. The change in length due
to compression or extension between individual
measur- ing bars are taken by measuring the
depth of the near end of the respective measur-
ing bars from a reference plate provided at the
mouth of the borehole. A digital
calliper/micrometre depth gage with a resolution
of 0.01 mm is used to take the readings.
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