2. Introduction
• A clinometer or inclinometer is an instrument
for measuring angles of slope (or tilt),
elevation or depression of an object with
respect to gravity.
• Slope inclinometers/indicators are used to
determine the magnitude, rate, direction,
depth, and type of landslide movement.
3. Fig: Principles of inclinometer configuration of
inclinometer equipments
Illustration of inclinometer operation
(modified from Dunnicliff 1988 and Slope
Indicator 2005)
5. Inclinometers
• Inclinometers are also known as slope gauge,
gradient meter, slope alert, tilt meter
• Their main function includes measurement of
the angle of depression as well as elevation
with reference to gravity and it also includes
measuring the angle of slopes that are positive
as well as negative.
6. In Landslide Monitoring
Slope inclinometers helps in measuring
• Direction of movement.
• Rate of movement.
• Magnitude and location of movement.
First, the bottom of the inclinometer must be located well below the
potential zone of movement so the bottom of the inclinometer does not
translate. If the inclinometer is not located well below the zone of
movement, the inclinometer will not capture the total amount of
movement. In other words, the inclinometer that is too shallow can
yield too small of a movement, if any, when compared to sufficiently
deep inclinometers.
Instalation of Slope Inclinometer
7.
8. Inclinometer Casing
• An inclinometer system has two components:
• (1) inclinometer casing and
• (2) an inclinometer measurement system.
• Inclinometer casing provides access for subsurface
measurements. Grooves inside the casing control the
orientation of the inclinometer sensor and provide a
uniform surface for measurements.
• Inclinometer casing is usually installed in a borehole. It
can also be embedded in fill, buried in a trench
(horizontal inclinometers), cast into concrete, or
attached to a structure.
9. Digitilt Classic Inclinometer System.
The Digitilt Classic system includes the Digitilt probe,
heavy-duty control cable, the DataMate readout,
and DigiPro2 software. Other classic components
include a horizontal probe, a spiral sensor, and a
portable tiltmeter.
Digitilt Probe
The classic Digitilt probe has earned a world-
wide reputation for durability, high precision,
and rapid response. It employs two force-
balanced servo accelerometers manufactured
by Slope Indicator.
Classic Control Cable
Classic control cable is durable and easy to
handle. It remains flexible in cold weather, resists
chemicals and abrasion, and provides excellent
dimensional stability. Flexible rubber depth
marks are permanently vulcanized to the cable
jacket.
10. Operation
• The in-place inclinometer system consists of inclinometer casing
and a chain of inclinometer sensors. The inclinometer casing,
which controls the orientation of the sensors, is installed in a
trench or horizontal borehole with one set of grooves oriented
vertically. The sensors are then positioned within the casing.
• The sensors measure the inclination of the casing (tilt from
horizontal). Changes in the inclination readings indicate that the
casing has been displaced by ground movement. The amount of
displacement is calculated by finding the difference between the
current inclination reading and the initial reading and then
converting the result to a vertical distance.
11. Applications
• Determining the angle of the Earth's magnetic field with
respect to the horizontal plane.
• Showing a deviation from the true vertical or horizontal.
• Surveying, to measure an angle of inclination or elevation.
• Alerting an equipment operator that it may tip over.
• Measuring angles of elevation, slope, or incline, e.g. of an
embankment.
• Measuring slight differences in slopes, particularly for
geophysics. Such inclinometers are, for instance, used for
monitoring volcanoes, or for measuring the depth and rate
of landslide movement.
• Measuring movements in walls or the ground in civil
engineering projects.
12. Application Contd…
• Detecting zones of movement and establish whether movement is
constant, accelerating, or responding to remedial measures.
• Checking that deformations are within design limits, that struts
and anchors are performing as expected, and that adjacent
buildings are not affected by ground movements.
• Verifying stability of dams, dam abutments, and upstream slopes
during and after impoundment.
• Monitoring settlement profiles of embankments, foundations, and
other structures (horizontal inclinometer).
• Monitoring of ground movements induced by tunnel construction
and excavation.
• Monitoring of stabilization measures such as grouting and
underpinning.
• Monitoring settlement under tanks, landfills, embankments, and
dams.
13. Inclinometer accuracy
The precision of inclinometer measurements depends on several factors such as them
design of the sensor and quality of the casing, probe, cable, and readout system.
Bias-shift error
• The sensor bias is the reading of the probe when it is vertical. Initially, the sensor
bias is set close to zero in the factory, but it may change during field use. If the
sensor bias is zero, the readings of A0 and A180 should be numerically identical but
opposite in sign. Thus, the magnitude of the bias shift can be evaluated using the
checksum, which should be zero if there is no bias shift.
Sensitivity drift
• The causes of sensitivity drift are a drift in the operation amplifier in the pre-amplifier of the
probe. The sensitivity drift is directly proportional to the magnitude of the readings, and it
varies between data sets but is relatively constant for each data set
Rotation error
• The rotation error occurs when the inclinometer casing deviates significantly from vertical. If
the accelerometer sensing axis in the A-axis is rotated slightly towards the B-axis, the A-axis
accelerometer will be sensitive to inclination in the B-axis.
Depth positioning error
• The depth positioning error results from the probe being positioned at different depths than
the “zero” readings in the casing. The difference in the vertical position of the probe is
usually caused by a change in the cable reference, cable length, and/or compression or
settlement of the casing
14. Summary
• Slope inclinometers are used to determine the vitally
important magnitude, rate, direction, depth, and type of
landslide movement. This information is used to understand
the cause, behavior, and remediation of a landslide. However,
many inclinometer measurements fail to achieve these
intended aims because of lack of appreciation of the many
factors that need to be correctly implemented during
installation, monitoring, and data reduction.
• The installation factors include ensuring the bottom of the
inclinometer is located in stable ground, the use of the proper
backfill to fix the inclinometer in the slide mass, and the use of
a flexible casing so it can detect small amounts of movement.
• The systematic errors that need to be considered in the data
reduction phase include the bias-shift error, sensitivity drift,
rotation error, and depth positioning error.
