ASTM D6230-98
(Test Method)Standard Test Method for Monitoring Ground Movement Using Probe-Type Inclinometers
Standard Test Method for Monitoring Ground Movement Using Probe-Type Inclinometers
SCOPE
1.1 This test method covers the use of inclinometers to monitor the internal movement of ground. The test method covers types of instruments, installation procedures operating procedures and maintenance requirements. It also provides formulae for data reduction.
1.2 The values stated in SI units are to be regarded as the standard. The inch-pound units given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation:D6230–98
Standard Test Method for
Monitoring Ground Movement Using Probe-Type
Inclinometers
This standard is issued under the fixed designation D 6230; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope monitoring the magnitude and rate of horizontal movements
for embankments and excavations, monitoring the settlement
1.1 This test method covers the use of inclinometers to
and lateral spread beneath tanks and embankments, and moni-
monitor the internal movement of ground. The test method
toring the deflection of bulkheads, piles or structural walls.
covers types of instruments, installation procedures, operating
procedures and maintenance requirements. It also provides
4. Apparatus
formulae for data reduction.
4.1 The probe type inclinometer uses sensors inside a probe
1.2 The values stated in SI units are to be regarded as the
to indicate the orientation of the probe relative to the pull of
standard. The inch-pound units given in parentheses are for
gravity. The complete system consists of:
information only.
4.1.1 A permanently installed pipe, called casing, with test
1.3 This standard does not purport to address all of the
method grooves. The casing is made of plastic, aluminum
safety concerns, if any, associated with its use. It is the
alloy, or fiberglass.
responsibility of the user of this standard to establish appro-
4.1.2 The Probe—Most probes use force balance acceler-
priate health and safety practices and determine the applica-
ometers which give a voltage output that is proportional to
bility of regulatory limitations prior to use.
inclination of the probe. Biaxial probes contain two sensors
2. Referenced Documents oriented 90 ° apart to permit readings in orthogonal directions
at the same time.
2.1 ASTM Standards:
4.1.3 A portable readout unit with power supply for the
D 653 Terminology Relating to Soil, Rock, and Contained
sensors and display to indicate probe inclination. The readout
Fluids
unit may have internal memory to record data.
D 4622 Test Method for Rock Mass Monitoring Using
4.1.4 An electrical cable connecting the probe and readout
Inclinometers
unit with distance markings. Fig. 1 shows a typical set of
3. Significance and Use
components.
3.1 An inclinometer is a device for measuring deformation
5. Procedure
normal to the axis of a pipe by passing a probe along the pipe
5.1 Installation of Casing in a Borehole:
and measuring the inclination of the probe with respect to the
5.1.1 Select casing materials that are compatible with the
line of gravity. Measurements are converted to distances using
environmental conditions at the installation. Select casing size
trigonometric functions. Distances are summed to find the
consistent with the specific measurement requirements and
position of the pipe. Successive measurements give differences
conditions for the job. Store casing materials in a safe, secure
in position of the pipe and indicate deformation normal to the
place to prevent damage. Sunlight may damage plastic casing.
axis of the pipe. In most cases the pipe is installed in a
HighandlowpHmaydamagemetalcasing.Notethataspecial
near-vertical hole. Measurements indicate subsurface horizon-
probe may be required for non-vertical boreholes.
tal deformation. In some cases the pipe is installed horizontally
5.1.2 Assemble all components required for the casing,
and the measurements indicate vertical deformation.
including casing, joints, connectors, and end cap. Examine
3.2 Inclinometers are also called slope inclinometers or
each component for defects. Do not use defective components
slope indicators. Typical applications include measuring the
since they may later cause problems with readings that are
rate of landslide movement and locating the zone of shearing,
difficult to diagnose and impossible to correct. Keep all
components clean and free of foreign matter during assembly.
This test method is under the jurisdiction of ASTM Committee D-18 on Soil Follow the manufacturer’s instructions for assembly of the
and Rock and is the direct responsibility of Subcommittee D18.23 on Field
casing. If required, use sealing mastic and tape to seal all
Instrumentation.
couplings to prevent later flow of soil particles into the casing.
Current edition approved Feb. 10, 1998. Published January 1999.
Annual Book of ASTM Standards, Vol 04.08.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D6230–98
techniques to prevent leaving large voids in the backfill. Such
voids can later lead to erratic readings. Place backfill and
withdraw drill casing or augers in sequence to prevent any
squeezing off of the borehole. Withdraw drill casing and
hollow-stem augers without rotation to prevent damage to the
inclinometer casing. Use measures to prevent backfill from
spilling into the inclinometer casing.
5.2 Installation on The Ground Surface of Horizontal Cas-
ing:
NOTE 1—A practical limit for installing horizontal casing is about 100
m. Beyond 100 m cable friction makes it difficult to pull the inclinometer
probe through the casing. Special Teflon inserts on the cable alleviate the
problem to some degree.
5.2.1 Select casing materials that are compatible with the
environmental conditions at the installation. Select casing size
consistent with the specific measurement requirements and
conditions for the job. Store casing materials in a safe, secure
place to prevent damage. Sunlight may damage plastic casing.
FIG. 1 Typical Components of Inclinometer System
HighandlowpHmaydamagemetalcasing.Notethataspecial
probe is required for horizontal casing. If one end of the casing
istobeburiedthentheendcapcontainsapulleytocarryawire
Thisisespeciallyimportantwhenusinggrouttosealthecasing
that is used to pull the probe into the inclinometer casing.
in the hole. Exercise care to keep the casing grooves free of
Special care must be taken to insure that the pulley is correctly
obstructions. When assembling couplings, use procedures to
assembled, free to turn and has the wire in place. Take
prevent spiraling of the casing grooves. Twist adjacent cou-
precautions at all times during installation to keep the wire
plings in alternate directions before fixing to minimize spiral-
clean.
ing. Examine the casing during assembly to confirm that
5.2.2 Create a near-level surface over the length where the
spiraling is not occurring. Place a cap on the bottom end and
casing is to be installed. Cover with a bed of at least 50-mm
seal it to prevent inflow.
(2-in.) deep and 300-mm (12-in.) wide of clean sand, pea
5.1.3 Create the borehole using procedures to keep it
gravel or a lean grout.
aligned within the range of the readout equipment. Extend the
5.2.3 Assemble all components required for the casing,
borehole at least 5 m (16 ft) beyond the zone of expected
including casing joints, connectors, and end cap. Examine each
movement. It may be necessary to use casing, hollow-stem
component for defects. Do not use defective components since
augers, or drilling mud to keep the hole open and stable. Flush
theymaylatercauseproblemswithreadingsthataredifficultto
the hole until clear of drilling cuttings.
diagnose and impossible to correct. Keep all components clean
5.1.4 Insert the casing into the borehole. Establish the
and free of foreign matter during assembly. Follow the manu-
reference orientation for the casing and align one set of groves
facturer’s instructions for assembly of the casing. If required
with this reference.This orientation is commonly referred to as
usesealingmasticandtapetosealallcouplingstopreventlater
the A direction. It should align with the direction of greatest
flow of soil particles into the casing. This is especially
anticipated movement. Add clean water to the casing if
important when using grout to seal the casing in the borehole.
necessary to overcome buoyancy. Use care to minimize any
Exercise care to keep the casing grooves free of obstructions.
twistofthecasingduringinstallation.Careshouldbeexercised
When assembling couplings, use procedures to prevent spiral-
to maintain orientation without twisting from the first piece of
ing of the casing grooves.Twist adjacent couplings in alternate
casing to the last. Twisting the top of the casing may cause
directions before fixing to minimize spiraling. Examine the
spiraling of casing at depth.
casing during assembly to confirm that spiraling is not occur-
5.1.5 Backfill the annular space between the borehole wall
ring.
and the inclinometer casing with a suitable filling material.
5.2.4 Place the casing onto the bed and adjust its position
Borehole can be pre-grouted or post-grouted. If post-grouted,
grouting can be through a tremie placed in the annulus of the until it is within the tolerances required by the readout device.
Establish the reference orientation for the casing and align one
inclinometer casing and the borehole’s walls or via an internal
tremie connected to a one-way bottom grout valve. Options set of groves with this reference. This orientation is commonly
referred to as the A direction. It aligns with the direction of
includecementgrout,sandandpeagravel.Aleancementgrout
backfill is preferable unless the surrounding ground is too greatest anticipated movement. Visually check for and remove
any spiraling. Determine that the pull cable is in position and
pervioustoholdthegrout.Placegroutwithatremie.Buoyancy
moves freely through the inclinometer casing.
must be overcome with grout backfills. Add a weight to the
bottom of the inclinometer casing, temporarily place clean drill 5.2.5 Use hand tools or light construction equipment to
pipe inside the casing, or place the first 3 m (10 ft) of grout place clean sand, pea gravel or lean grout evenly, at least
aroundthebottomofthecasingandletitset,thencompletethe 150-mm (6-in.) wide, on both sides of the casing. Cover the
grouting. Place sand and gravel backfills slowly and with inclinometer casing with at least 50 mm (2 in.) of clean sand,
D6230–98
pea gravel or lean grout. Place fill over casing in 150-mm the set of readings. For uniaxial probes, two more traverses
(6-in.) lifts. Fill for the first lift should not contain any particles must be made for the B direction the same way as for the A
direction.
larger than 25 mm (1 in.). If compaction is required, use hand
compactors for the first two lifts.
5.4.2 Check the set of readings by summing the readings for
the A and A8 directions at each depth and the readings for the
5.3 Calibration:
B and B8 direction. These sums are called check-sums and
5.3.1 Inclinometers are factory calibrated and supplied with
should equal a constant value that is a characteristic of the
a calibration factor, K, that is specific to the probe and the
probe. Refer to the manufacturer’s literature for information on
readout unit. Some manufacturers provide standardized read-
allowable variation in the check-sum. A single deviation in a
out units that can be used with multiple probes. However it
check-sum probably indicates a bad reading. Erratic behavior
should be noted that electronic variations in the readout
of the check-sums generally indicates a poor electrical connec-
equipment may cause conditions where different probes will
tion or a malfunctioning probe or readout.
give different readings. It is recommended that a calibration
5.5 Initial Readings:
check be performed any time a probe and readout unit
5.5.1 Makeinitialobservationsafterallowingsufficienttime
combination is changed. For applications involving small but
for the grout around the casing to set or for the backfill to
important changes over several years, recalibrate the instru-
stabilize. Since computation of all displacements is based on
ment to the precision of the device at least once per year.
theinitialreadings,itisimportanttohaveavalidset.Verifythe
5.3.2 Perform a calibration check before each set of incli-
initial set of readings with at least two sets of readings, taken
nometer readings. Field checks can be made using a test stand,
on the same day. Check these readings for stability of the
a test casing, or a section of field casing in material that does
check-sums and for displacement within the accuracy of the
not move. Test stands are available from most manufacturers.
equipment. Repeat observations until satisfactory agreement is
They employ a short piece of inclinometer casing preset at a
obtained. From all initial readings taken, one set should be
fixed angle. The test stand must be set on a stable base and
selectedforuseasthereferencesetforallsubsequentreadings.
properly aligned by the manufacturer’s instructions. A test
Take readings on any spiral with a spiral sensor if corrections
casing is a short piece of casing installed in a fixed position
for twist are desired, or if there is potential for twist in the
with the grooves at angles of 0 to 10° from the vertical. A
casing of sufficient magnitude to affect the computed displace-
section of field casing that is placed in fixed material can be
ments of the casing.
used to check calibrations. This last method is the least
5.5.2 Thetopposition(x,yandz)oftheinclinometercasing
preferable since most field casings are near-vertical (or near-
must be located by survey at the same time initial readings are
horizontal). Calibration checks on vertical casing can indicate
made by survey to the accuracy of the inclinometer readings.
malfunctioning equipment but cannot provide an accurate
Later changes in the top position of the casing can be used to
calibration.
check the inclinometer readings or to correct for movement of
5.3.3 Perform a calibration check by assembling the probe,
the bottom of the inclinometer casing.
cable and readout equipment and allowing it to equilibrate to
5.6 Observations:
ambient temperature for at least 10 min. The probe is posi-
5.6.1 The frequency of observations depends upon the rate
tioned in the test stand or casing and readings taken.The probe
ofmovementandtheallowablemovements.Someinstallations
is removed, rotated 90°, reinserted and read. This operation is
mayrequireseveralreadingsperday.Othersmayrequireafew
repeated to obtain readings at 180 and 270°. Consult the
readingsperyear.Inuncertainconditions,inclinometercasings
manufacturer’s instructions to determine if your readings are
should be read frequently just after installation and the results
within the recommended ranges for the equipment. Any
used to adjust the interval of subsequent observations. Obser-
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