IS 14395: Guidelines for monitoring of rock movements using probe inclinometer

13 Pages·1996·1.1 MB·English

by  Bureau of Indian Standards

इंटरनेट मानक
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in order to promote transparency and accountability in the working of every public authority,
and whereas the attached publication of the Bureau of Indian Standards is of particular interest
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education and knowledge, the attached public safety standard is made available to promote the
timely dissemination of this information in an accurate manner to the public.
“जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न’ 5 तरफ”
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“The Right to Information, The Right to Live” “Step Out From the Old to the New”
IS 14395 (1996): Guidelines for monitoring of rock
movements using probe inclinometer [CED 48: Rock Mechanics]
“!ान $ एक न’ भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
““IInnvveenntt aa NNeeww IInnddiiaa UUssiinngg KKnnoowwlleeddggee””
“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै”
Bhartṛhari—Nītiśatakam
“Knowledge is such a treasure which cannot be stolen”

IS 14395 : 1996
12
Reaffirmed 20

~~q)f~~
~~~Cf>RT-~
Indian Standard
MONITORING OF ROCK MOVEMENTS
USING PROBE INCLINOMETER —
GUIDELINES
ICS 07.060
© BlS 1996
BUREAU OF INDIAN STANDARDS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002

September 1996 Price Group 3
A~ND~NTNO. 1 DECEMBER 2006
TO
IS 14395: 1996MONITORINGOF ROCK
~[OVE~NTSUSINGPROBEINCLINOMETER
GUIDELINES
(Page1,clause2.1,line9)- Substitute 'reusable'lor'usable'.
(Page 1,clause1.2.2)- Substitute 'Ea' for 'E'.
(Page 1, clause 2.2.3, last line) - Substitute 'radiotelemetly' lor
'nedioelemetry '.
(Page2,Fig.1)- Substitutethefollowingfortheexistingfigure:
~UT
1
"UNlT1
GRAOUI,TED
ELECTRiCAl
CABLE"'___ ,-!LSinSe
"'
PROBE CONTAINING /"
GRAVITV-5ENSING ,\
TRANSDUCER : DISTANCEBETWEEN L
Y /TRUE
SUCCESSIVEREADINGS , VERTICAL
COlJPLlNG
KEYWAY
GUIDE
CASING
REFERENCE
FIo. 1PROBEINCUNOMETER
1
AmendNo.1toIS14395: 1996
(Page 2~clause3.2(h),line1]- Substitute'robust' lor 'rebust'.
{Page 3,clauseS(c),line3]- Substitutecdetailed~lor 'details'.
(CED48)
Reproppbyunit,81S,NewDelhi.IDdia
Rock Mechanics Sectional Committee, CED 48
FOREWORD
This Indian Standard was adopted hy the Bureau of Indian Standards, after the draft finalized by the Rock
Mechanics Sectional Committee had been approved by the Civil Engineering Division Council.
Monitoringofrock movements isdone toensuresafetyduringconstructionand operation. It helps inreceiving
a fore-warning of the impending failure and taking corrective measures. One of the methods to monitor
the movement of rock is by using inclinometer.
In the formulation of this standard, assistance has been derived from the suggested method of International
Society of Rock Mechanics,
Technical Committee responsible for the formulation of this standard is given in Annex A.
For the purpose of deciding whether a particular requirement of this standard is complied with, the final
value, ohserved or calculated, expressing the result of a test, shall be rounded off in accordance with
IS 2 : 1960 ..Rules for rounding off numerical values (revised)'. The number of significant places retained
in the rounded off value should be the same as that of the specified value in this standard.
IS 14395 1996
Indian Standard
MONITORING OF ROCK MOVEMENTS
USING PROBE INCLINOMETER
GUIDELINES
1 SCOPE (LC)..Jn
f=
1.1 This standard covers one of the methods of 21t
monitoringrockmovementswhereaboreholeiseither
where L is the self-inductance and C the
available or drilled and a probe inclinometer is used.
capacitance of the solenoids. A relative
2 MONITORING SYSTEMS displacement, d, of the inner and outer
solenoids produces achange in the measured
2.1 The instrumentation system for monitoring rock resonant frequency, f, such that
movements using probe inclinometers shall generally
have three components. A probe which responds to d=K( (1j/ )~
1-
the rock movements, a transmitting system which
mayuserods,electricalcables,radiotelemetrydevices,
etc, for transmitting the sensor output to thereadout wherefa is the calibrated frequency for the
location. Areadout/recording unitsuchasdialgauges, null position and K is a constant. Several
digital display, magnetic tape recorder etc, which of the bore hole extensometers and
converts the data in usuable form for the user. inclinometers are based on this principle.
Theseinstrumentsmaybereadremotelyusing
2.2 Probes Usedfor MonitoringRock Movements
radioelemetry.
2.2.1 Probes withElectricResistanceStrainGauges
3 PRINCIPLES OF OPERATION OF PROBE
These operate on the principle that the resistance of INCLINOMETERS
a wire changes proportionately with strain. In strain
gauge systems, strain gauges made from thin wire or 3.1 The instrument measures ground movements
foil, are honded to a cantilever spring. Changes in only indirections perpendicular to the borehole axis.
theinclinationoftheprobeareaccompaniedbychanges Most of the available instruments are designed to
in the strains and resistances of the strain gauges operateinnearvertical boreholes, inwhichcase only
which are read using a Wheatstone bridge circuit. horizontal movements can be recorded.
2.2.2 Probes with Vibrating Wire Sensors Theprobe inclinometergives acompleteanddetailed
profile of displacement, along the borehole, in the
These are based on the factthat the natural frequency
ofvibrationofastretched wiredepends onthetension lateral direction.
in the wire. Vibrating wire transducer shan contain
Howeversuch inclinometer system isnotsuitable for
two electromagnets, one of these is the exciter and
continuous or remote reading.
the other acts as a pick up. When the wire is forced
to oscillate, an alternating current is induced in the
3.2 Apparatus
second electromagnet which has the same frequency
asthe natural frequency of the vibration of thegauge a) A probe inclinometer shallconsist of a probe
wire. The signal when amplified provides a or torpedo fitted with guide wheels and
measurable quantity in terms of frequency. Once containingagravity-operatedtiltsensor which
this frequency is known, any physical quantity can generatesanelectricalsignalandisconnected
be calculated using calibration schemes. The strain hy an electrical cable to a power source and
in the gauge and its frequency of vibration are readoutboxforrecordingtheangleebetween
expressed as: the probe axis and the vertical (Fig. I). The
probe shall operate in a guide tube grouted
=
e into a borehole tNx size), the probe being
lowered in stages and the tilt measured at
where
= eachstage. AsshowninFig. 1,measurements
C gauge constant,
of tilt and probe depth shall be used to
e = strain,
= compute horizontal deviations of the guide
L length of wire,
tubefrom true vertical. Differences between
p = density of wire material,
= successivesetsofmeasurementsshallindicate
E modulus of elasticity of gaugewire,
= horizontalmovementoftheentireguide tube.
~l zero strain vibrating frequency, and
J = vibrating frequency at strain. b) The guide tubing shape and dimensions shall
be designed to suit the probe to be used.
2.2.3 Self-inductance instruments. These are based Typically the tubing shall be constructed of
onthemutualinductanceofapairofcoaxialsolenoids plasticorepoxy-resin coated aluminium with
forming a circuit of resonant frequency. fourorthogonalinternalkeywaystoacceptthe
r-e=r-
IS 14395 1996
J., - READOUT
UNIT
GRADUATED
ELECTRICAl
-----1
CABLE ~--I LSin68
ACTUALALIGNMENT
PROBECONTAINING OFGUIDECASING
GRAVITY-SENSING -:
TRANSDUCEB ~ ~
5e
~
DISTANCEBETWEEN
BOREHOLE
SUCCESSrvE READINGS
TRUE
VERTICAL
KEY WAY
~,_GUIDE
GUIDE WHEELS
CASING
FIG. PROBE INCLINOMETER
probe guide wheels. Plastic casing may be guidewheels.Thesensingdevice isconnected
preferred for longlife, as itisprotected from by an electric cahle to acompatible readout
corrosion. Theguide tubeshall beassembled box.
forindividual lengthsoftubingupto3mlong
f) Themeasuringrange,sensitivity andaccuracy
with couplings which are butt-jointed or
of the probe with its readout box shall be
telescopic. Design 0.' the couplings, their
specified according to the specific
telescopic travel and methodoffixingmaybe
requirements of the project. Reproducibility
such that itallows the installed guide tuheto
of the equipment when operating under site
readilycompressorextendaxiallybyanamount
conditions in general, shall he kept equal to
equal to thegroundcompressionorextension.
or better than ±O.O1°.
Couplings shall bemadewatertighttoprevent
groutfromenteringtheguidetube. Telescopic g) The equipment shall he designed to ensure
couplings mayheusedwheresignificantaxial that the specified accuracy is maintained
movements are anticipated even though non irrespective of normal mechanical handling,
telescopicbuttcdcasingprovidebettertracking water pressures and corrosive environments
and easier depth reading control. encountered in usc.
The assembled guide tube should be h) The cable shall he rcbust and functional
sufficiently flexible to follow changes in withoutleakageorexcessive stretching under
horehole curvature caused by ground the tension that results frorn friction and
movements. In use, the tubing should not from the weight of cable and probe. The
substantially affect the magnitude of ground cable shall he permanently and clearly
movements, norshoulddistortionorbuckling graduated to enable measurement of probe
of the tube occur to an extent that impedes position with an accuracy better than 5 mm
free passage of the probe. or +0.05 percent of the depth at which the
prohe is to operate, whichever is greater. ,
c) Keyways in the assembled guide tuhe shall
be such that they allow free passage of the j) Calibrating device enables frequent checking
inclinometer probe. The keyways ideally of the equipment. Such calibrating devices
should be straight so that the probe does not allows the probe to be set in a section of
rotate about its axis by more than 1() in any guidetubeidentical tothatinwhichtheprobe
3 01 of travel in the installed tube, and istooperate; theinclination of theguide tube
preferablybynotmorethan5°inthecomplete heingadjustablefromverticaltothemaximum
assembled length. operating angle of the probe, with at least
oneintermediatesettingeithersideofvertical.
d) Grouting material shall be placed to
The calibrator should have an independent
completely filltheannular space betweenthe
angle measuring device of accuracy better
guide tube and.the borehole, the set grout
than 0.01°.
generally having a rigidity comparable with
thatof therockin whichthetube is installed. 4 PROCEDURE
e) The probe shall comprise of a cylindrical
4.1 Preparatory Investigations
housing withspring-loaded wheel assemblies
set typically 1/2 m or 1 m apart to locate Inclinometer borehole locations and depths shall be
it in the guide tube keyways. The housing selected on the basis of a study of the geotechnical

shall contain a tilt sensor to measure the features of the site, taking into consideration the
anglebetweentheprobeaxisandthe vertical, directions and magnitudes of anticipated ground
this angle being measured intheplane of the movements.
2
IS 14395 : 1996
4.2 Installations j) The probe shall be inserted with its guide
wheels in one pair of keyways and lowered
a) Boreholes shall be drilled to the full depth
to the bottom of the hole. A measuing
ofmeasurementatrequiredlocations. Ifsteel tranverseshallbemadestartingatthebottom
casing is used to maintain the hole open, it
comprising measurements at intervals along
shall be fully withdrawn in the course of
thecomplete length ofguide tubing, withthe
installing the guide tube.
probe held stationary at each measuring
b) Priortoinstallationofguidetubingtheground location while readings of the depth and
conditions shall beestablished by inspection inclinometerdisplayshallberecorded. These
of the core and/or the borehole. A shall be tabulated together with information
comprehensive geotechnical borehole Jog on the date, time, location, direction and
shall be compiled with particular attention keyway identification. The measurement
being given to zones of potential movement. interval,ingenera),iskeptequalto thespacing
between probe guide wheels although
c) The guide tube lengths shall be assembled, readings may be taken at twice this interval
each correctly oriented and inserted in the in many cases with little loss of accuracy.
borehole. The base tube shall be fitted with
a watertight cap. If vertical movements are k) Theprobeshallbewithdrawn,rotatedthrough
anticipated all couplings should be free to 1800 and re-inserted with its guide wheels
telescope and should be sealed to prevent in the same pair of keyways and lowered to
ingress of grout. If the borehole is full of thebottomof the hole. A second measuring
water or drilling mud, or if it is pre-filled traverse shall be completed as described in
with grout, the guide tubing may be filled above. Measuring locations shall be kept
with clean water to facilitateinsertion. If the identical to those for the first traverse, in
tubing is inserted in a dry hole, its weight which case the face error for pairs of
shouldhecarried hyanexternaltiewirefixed corresponding readings is determined which
tothelowerendoftheguidetubeandbanded shouldberelativelyconstantateverylocation.
to it at intervals. This provides an important field check on
data reliability.
d) After insertion is complete, the azimuth of
the guide tube keyways should be recorded In) If required, two further measuring traverses
toanaccuracy of±3°. Theguidetubeshould shall be made, as above hut with the probe
then beclamped in position and if necessary guide wheels in thesecond pairof keyways.
checked for spiral with a spiral measuring
probe. 5 DATA PROCESSING
e) The annular space between guide tube and a) All data should be processed as quickly as
borehole shall be grouted. In water-filled possible after taking readings.
holes,atrernicpipewillberequiredtoprevent b) Thefielddatashallbescrutinizedandohvious
mixing of water and grout and in deep errors marked on the field data sheet. If
horeholcs such a pipe is mandatory. correctionsarc made, theseshouldheclearly
Disposable grout valves are available which noted.
permit grouting from inside the guide tube
through the drill rod. After grouting, the c) Pairs of opposite-face readings shall he
interior of the guide tube should be flushed averaged to correct face error. The sign
withcleanwaterandmay,inaddition,require convention and details procedure used in
hrushing. The water may be left in place reducing data varies so that manufacturers'
or the tube 111Uy be pumped dry after the manualsshould hescrutinizedcarefully. The
direction of movement must be carefully
grout has set.
checked and recorded.
f) A protective lockable cap or cover should
d) Corrected readings shall be subtracted from
heinstalledovertheexposedendoftheguide
tubetoprevententryofdebrisanddiscourage initialreadingsatthesameguidetubelocation
todeterminetheincrementalchanges inangle
vandals. Positions and elevations of guide
or displacement.
tube collars to be used as a reference for
depth measurements should be noted and c) These incremental changes in angle
recorded to an accuracy of ±5 InITI. (88 degrees)may, ifrequired, heconverted
into incremental displacements (~. in 111m)
g) The probe should be checked at site both
using the Iorlowing formula:
before and after each day's readings.
Instrument malfunction should be promptly ~ = L sin 88
investigated and corrected and a diary of (where L in mill is the distance between
calibrations and adjustments should be kept. successive readings).
Unnecessary adjustment must be avoided.
f) Incremental angle or displacement changes
h) Several sets of initialreadings shall betaken shall be then summed, normally from the
immediately after the grout has set. These bottomoftheguidetube,inordertoconstruct
readings shall be averaged to provide a a graphical plot of total displacement versus
baseline for all subsequent observations. depth. It is often useful to plot incremental
Thereafter readings maybe takenat intervals angular (displacement) changes with depth
on the basis of site requirements. to indicate movement zones.
3