Role of Instrumentation in Slope Monitoring A Case Study

Volume 11, Issue 3, March 2023 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
Role of Instrumentation in Slope Monitoring:

A Case Study
1
R.S. Sehra (Scientist-D); 2Vipin Kumar (Assistant Research Officer)
Central Soil and Materials Research Station,
New Delhi
Abstract:- Unstable and high cutting rock slopes are D. Wedge failure:
inevitably encountered during the construction of dams, The wedge failure is also referred to as block failure or
powerhouses, quarries, highways, housing developments plane slope failure and it occurs along an infinite plane. It
works, etc. in the mountainous regions. Monitoring of mostly happens when the wedges and distinct blocks of the
these slopes through instrumentation and using soil mass get separated. It is also common when there is a
transmission technology may provide immediate soil layer that has the weak bearing capacity, joints, or
warning to people living in these areas from hazards. fissures and the slope has two different materials.
Many types of instruments such as extensometers, tilt-
meters; inclinometers etc. and their data transmission This is similar to translation failure and the main
systems are available for such monitoring. Types/causes difference is that the translation failure occurs in the
of slope failure and need/importance of geotechnical situation of the finite slope only but the wedge failure occurs
instrumentation have been discussed in this paper. In in both conditions (finite and infinite slopes).
addition, a case study of slope monitoring of Vyasi dam
powerhouse through instrumentation has been also  Some of the major causes are defined briefly as follows:
presented.  Earthquake.
 Rainfall.
I. INTRODUCTION  Erosion.
 Construction Work.
Unstable slopes affect almost every state in all types of  Geological characteristics.
geographies, whether the slopes are owned embankments  External loading.
and cut slopes or hazards originating from beyond-the-right-
of-way. It is classified into four types:  Effects of Slope Failure:
 Slope failure causes landslides that may cause loss of
A. Rotational failure: life and properties.
 Face or slope failure: This failure occurs on the surface  It reduces the bearing capacity of the soil.
of the slope which is passed through the toe of the slope.  Damage to the road causes slope failure.
It happens when the soil is above the toe which contains  It significantly affects humans and their lives.
weak strata.
 Toe failure: This is the most common type failure in  Prevention of Slope Failure:
which the failure plane is passed through the toe of the Following measures are taken to preventing the slope
slope. failures:
 Base failure: The failure which is occurred in the weak  Proper drainage to reduce the waterlogging and seepage
soil strata and failure plane passes through of base of the forces.
slope is called base failure.  Benching
 Terracing
B. Translational failure:
 Build retaining walls
This type of failure occurs in an infinite slope (the slope
 Rock bolts to maintain the stability of rock.
which has no boundaries) in which the movement of the soil
is along the level surface. It happens, mostly in the layered  Plantation
material, usually fail along geologic discontinuities such as II. SLOPE MONITORING BY
faults, joints, bedding surfaces, or the contact between two INSTRUMENTATION
rock types. They move out or down along a planar surface
with little tilting, and can travel great distances. The two most important parameters to monitor by
instrumentation are groundwater levels and displacement
C. Compound failure: those influence the stability of slope. Piezometers allow the
It is the combination of translation and rotational failure. determination of ground water levels and extensometers,
In this condition, the failure surface is curved at two ends, inclinometers, and tilt-meters allow determination of
and plain at the middle portion, and generally, this happens, direction and rate of slope movement an indication of
when the hard stratum is below the toe at considerable displacement magnitude.
depth.
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ISSN No:-2456-2165
A. Piezometers: vibration can be sensed by the electromagnetic coil and is
Piezometers should be considered at sites where frequent transmitted to a readout device. One end of the sensing wire
groundwater measurements are required (e.g. a site where is attached to a diaphragm that can be deformed by water
rapid groundwater fluctuations are suspected or where pressure entering through a porous tip. An increase in water
measurements are required during a critical event i.e. pressure from elevated piezo-metric levels reduces the
rainfall etc.). Vibrating wire piezometer shows in figure 1, tension in the wire by deforming the diaphragm inward. The
works on the same principle as tuning a guitar or piano magnetic coil in the piezometer “plucks” the wire to vibrate
(SINCO, 1994). it. The wire is plucked using variable excitation frequencies
and then allowed to return to its natural frequency. The
A steel wire is stretched over a distance. The wire is magnetic coil then acts as a sensor which is used to “count”
set to vibrating by “plucking” it with an electromagnetic the number of vibrations. The output signal is then
field. The natural frequency of the wire is a function of the converted into units of pressure or head.
tension in it. By reducing or increasing tension in the wire,
the frequency becomes lower or higher. The frequency of
Fig. 1: Vibrating Wire Piezometer
Probe inclinometers, “in-place” inclinometers, tilt- D. “In-Place” Inclinometers:

meters, and extensometers can be used alone or in “In-place” inclinometers can detect new movement, an
combination to monitor slope movement (Dunnicliffe, acceleration of movement, and the direction of movement.
1993). “In-place” inclinometers are installed in a borehole cased
with inclinometer casing. The wiring for the inclinometer
B. Inclinometers: can be buried and the boring covered with a locking cap to
It measures angles of inclination from the vertical in two vandal-proof the installation. The field setup of In-Place
planes oriented at 90° (orthogonal) to each other. The probe Inclinometer is shown in figure 2.
senses horizontal deviation between the probe axis and the
vertical plane, simultaneously in the ‘X’ and ‘Y’ directions.
C. Probe inclinometers:
These require manual operation while the other sensors
can be read electronically. The electronic sensors can be
coupled with a data logger for automated data collection.
These automated systems also can be combined with
telemetry to allow remote data collection. Additional
programming of the remote data collection system can be
used to trigger a warning of critical situations.

ISSN No:-2456-2165
Fig. 2: Field setup of In-Place Inclinometer
E. Tilt meters: device. They are an option for those sites that are too steep
Tilt-meters are also detected new movement, an for a drill rig or if the project budget does not allow for
acceleration of movement, and the direction of movement. drilling. Tilt-meters also can be covered with a vandal-proof
Tilt-meters are mounted at the ground surface. They may be enclosure and wires can be buried. Details of Tilt meter is
portable or fixed in place and they are rapid easy reading shown in figure 3.
Fig. 3: Details of Digital Tilt Meter
F. Extensometers: Movement of the slope pulls the weight along the graduated
Monitor axial movement /deformation in soil and rock at track. The amount and rate of movement can then be
various depths using rods of different lengths with reference measured manually. They are very inexpensive, but critical
to the instrument head shown in figure 4. Simple mechanical events can be missed if readings are not taken in a timely
extensometers use a steel wireline firmly connected to a fashion. These installations are also susceptible to vandalism
fixed location on the slope face on one end and to a track- and animal damage.
mounted weight, located off the slide, on the other end.

ISSN No:-2456-2165
Fig. 4: schematic arrangement of mechanical extensometers
G. Total Station: a particular point. Total station may also use for the
A total station is an electronic/optical instrument used in movement of the slope through monitoring some fixed point
modern surveying. The total station is an electronic in a slope. Figure 5 shows the Robotic Total Station with
theodolite (transit) integrated with an electronic distance Prism Targets.
meter (EDM) to read slope distances from the instrument to
Fig. 5: Robotic Total Station with Prism Targets

ISSN No:-2456-2165
III. TIME DOMAIN REFLECTOMETRY (TDR) to locate breaks and faults in communication and power
lines, its first geotechnical use was around 1980 to locate
Time domain reflectometry (TDR) is a relatively new shear zones in underground coal mines (Wade and Conroy,
approach to monitoring slope movement (Beck and Kane, 1980).
1996; Kane and Beck, 1994, 1996a, 1996b; Mikkelsen,
1996; O’Connor and Dowding, 1999). Originally developed
Fig. 6: Components of TDR system for monitoring slope movement
Time Domain Reflectometry is a technique in which  If water infiltrates a TDR cable, it will change the cable’s
electronic pulses are sent down a length of a coaxial cable electrical properties and may make signatures difficult to
which has been grouted in a drill-hole. When deformation or interpret.
a break in the cable is encountered, a signal is reflected
giving information on the subsurface rock mass deformation IV. INSTRUMENTATION CASE STUDY
shown in figure 6. TDR cables are gaining popularity and
have several advantages over traditional inclinometers Vyasi hydroelectric project of 120 (2×60) MW
(Kane, 1998): capacity is a run of the river scheme situated on river
 Lower cost of installation. Yamuna in Uttrakhand. The project consists of powerhouse
structures that require stability assessment. It is imperative
 Deeper hole depths possible.
that long term stability of these structures is ascertained
 Rapid and remote monitoring possible.
from geotechnical instrumentation program. Due to the
 Immediate deformation determinations. project settings in Himalayas, it is anticipated that the
 TDR readings can easily be automated. project may experience either rock burst conditions or
 Complex installations possible. squeezing ground conditions. Therefore, it is important to
measure deformation and rock pressure concurrently. The
Some Disadvantages also:
rock pressure measurements started since December 01,
 TDR cannot determine the actual amount of movement. 2020 near the power house. Measurements at all the places
Relative amounts can Kane and Beck - 6/20 be estimated. are continuously observed and their analysis is reported.
 The direction of movement cannot be ascertained from a Total nos. of instruments installed is given in table no.1 and
TDR signature. photographs are shown in figure 7 below:
 The cable must be deformed before movement can be
located. Simple bending of the cable, without damage,
will not indicate any movement.
Sr. No Type of the Instrument Quantity

1 Inclinometers 06
2 Piezometers 10
3 Load Cells 28
Total 44
Table 1: Details of Instruments

ISSN No:-2456-2165
Surface Power House & back slope Cables Anchors
Load Cell Junction Boxes/Nodes

Fig. 7: Photographs of instruments and junction boxes
Fig. 8: Schematic View of Inclinometer installation showing in X and Y Directions
V. DATA ANALYSIS AND INTERPRETATION
Fig. 9: Daily Variation in Pore Pressure Fig.10: Daily Variation in Load

ISSN No:-2456-2165
Fig. 11: Cumulative monthly deviations in IPI-3
VI. CONCLUSION Monitoring for Quarry Site of Sunni Dam, SJVNL,

District Shimla, Himanchal Pradesh, Indian
The daily variation of pore water pressure (MPa) of Institute of Technology (ISM) Dhanbad.
piezometer, load (ton) variation of load cell and monthly [4.] Jami M. Girard1 , P.E., C.M.S.P. “Assessing and
deviation with respect of depth of in-place inclinometer is Monitoring open pit mine high walls” Report on
shown graphically in figures 9, 10 and 11 respectively. “Time Domain Reflectometry for Monitoring Slope
Movements” Department of Civil and Architectural
As per the geology, folds, faults, joints, and stratified Engineering University of Wyoming 1000 E.
rocks are potential zones for the movement/ deformation University Avenue Laramie, Wyoming 82071
and storage of ground water. The pore water pressure is August 2006.
main affecting parameter in case of slope stability analysis.
The groundwater level has a major influence on material
behavior (drained-untrained), and changes in groundwater
level can result in settlements and damage to structures and
infrastructure. Geotechnical instrumentation plays an
important role in the monitoring of all such parameters like
deformation, ground water etc which affects the stability of
slope.
It is advisable to monitor the ground water level and

movement in the slope area by piezometers, probe
inclinometers; “in-place” inclinometers, tiltmeters, and multi
point borehole extensometers so that the destruction caused
by landslide can be drastically reduced by an effective
forewarning above system that can mitigate risks and loss to
human lives and infrastructure.
REFERENCES
[1.] William F. Kane, President and Principal Engineer,

KANE Geo Tech, Inc and Timothy J. Beck
Associate Engineering Geologist California
Department of Transportation “Instrumentation
practice for slope monitoring” Submitted for
Publication in: "ENGINEERING GEOLOGY
PRACTICE IN NORTHERN CALIFORNIA"
Association of Engineering Geologists.
[2.] Dunnicliff,J.,1993, Geotechnical instrumentation
for monitoring field performance: John Wiley &
Sons, Inc., New York, Project Report of Vyasi H.E.
Project (2 x 60 MW), Dakpathar, Dehradun
(Uttarakhand).
[3.] Slope Stability Report, Design, Numerical
Modeling, Kinematic Analysis, Slope Stability &
Protection Works Including Slope Health

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Volume 11, Issue 3, March 2023 International Journal of Innovative Science and Research Technology

Role of Instrumentation in Slope Monitoring:

IJISRT23MAR1420 www.ijisrt.com 2016

Fig. 1: Vibrating Wire Piezometer

Probe inclinometers, “in-place” inclinometers, tilt- D. “In-Place” Inclinometers:

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Fig. 2: Field setup of In-Place Inclinometer

Fig. 3: Details of Digital Tilt Meter

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Fig. 4: schematic arrangement of mechanical extensometers

Fig. 5: Robotic Total Station with Prism Targets

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Fig. 6: Components of TDR system for monitoring slope movement

Sr. No Type of the Instrument Quantity

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Surface Power House & back slope Cables Anchors

Load Cell Junction Boxes/Nodes

Fig. 8: Schematic View of Inclinometer installation showing in X and Y Directions

V. DATA ANALYSIS AND INTERPRETATION

Fig. 9: Daily Variation in Pore Pressure Fig.10: Daily Variation in Load

IJISRT23MAR1420 www.ijisrt.com 2021

Fig. 11: Cumulative monthly deviations in IPI-3

VI. CONCLUSION Monitoring for Quarry Site of Sunni Dam, SJVNL,

It is advisable to monitor the ground water level and

[1.] William F. Kane, President and Principal Engineer,

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