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Inclinometer DataInclinometer Data& &
Recognition of System ErrorsRecognition of System Errors
ByByP. Erik Mikkelsen, P.E.P. Erik Mikkelsen, P.E.
Consulting EngineerConsulting EngineerGeoMetronGeoMetron Inc PSInc PSBellevue, WA USABellevue, WA USA
(Graphics: Courtesy of Rick Monroe, Durham Geo(Graphics: Courtesy of Rick Monroe, Durham Geo--Slope Indicator)Slope Indicator)
Univ. of Florida Short Course, March 19, 2007Univ. of Florida Short Course, March 19, 2007
Installed Casing
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Inclinometer Casing
The Function of Casing
• Provides sub-surface access for measurements.
• Maintains orientation of probe.
• Provides flat surface for repeatable measurements.
•Grooves compatible with probe wheels
• Deforms with the surrounding ground.
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Glue & Rivet CouplingsAdvantages
• Very strong. High tolerancefor twisting and bending.
• Easy to extend or repair.
Disadvantages
• Needs glue, rivets, and tape.
• 2.57 / 70 mm diameter only.
Other
• Simple settlement couplings.
EPIC Casing
Shear-Wire CouplingsAdvantages
• Rapid assembly.
• Can be disassembled.
• Very strong.
• Self-sealing.
• Good in cold weather.
Disadvantage
Oversize couplings.
Other: 3 diameters.
CPI Casing
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Inclinometer Probe, Cable, Readout
From Tilt to Lateral Deviation
L x sine θ
L
θ
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Surveying the Casing
Plotting Lateral Deviation
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Deviation vs Displacement
Deviation:Casing profile
Displacement: Casing movement
Deviation Displacement
Displacement Graphs
Displacementvs Depth
Displacement vs Time
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A0A180 A–
Orientation of Probe, Casing, & Plot
A+
A- A+
Reading Units
English Units
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Reading Units
English Units
Example: Reading Units to Deviation
L= 24 in
θ
Deviation = L x A20000
= 24 in x 34920000
= 0.4188 in
English Units
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Difference & Probe BiasA0 at 1°
Ideal: 349 A180 at 1°Ideal: -349
Ideal Difference= 349 – (349)= 698
Actual Difference= 359 – (-339)= (349 +10) – (-349 +10)= 698
English Units
Actual: 359 Bias: +10
Actual: -339Bias: +10
Difference vs Checksums
Actual: 359Ideal: 349 Bias: +10
A0 at 1°
Actual: -339Ideal: -349Bias: +10
A180 at 1° Difference
= A0 – A180= 698
Checksum= A0 + A180= 359 + (-339)= 20
English Units
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Displacement
Displacement = Δ Deviation
= Deviation n – Deviation 0= L x Δ Algebraic Difference
40000
English Units
Graphing Inclinometer Data
Presentation Graphs • Displacement vs Depth
• Displacement vs Time
Diagnostic Graphs• Checksums
• Casing Profile
• Casing curvature
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Displacementvs Depth
• Incremental
• Cumulative
Incremental Cumulative
Displacement vs Time
Movement at selected zone, plotted against time.
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Presentation TipKeep your graphs simple and easy to understand.
ChecksumGraphs
Checksum Difference Checksum
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DiagnosticGraphs
• Casing Curvature
• Casing Profile
Curvature Profile
Graphing TipChoose scales that reveal appropriate information and hide noise.
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Accuracy
English Units
Total Error± 0.3 inch per 100 ft.
Random Error± 0.05 inch per 100 ft.
Systematic Error± 0.25 inch per 100 ft.
Limit of Precision± 0.01 inch per reading.± 0.05 inch per 100 ft.
Sources of Error
ReadoutSet upOperation
CasingInclination*Curvature*BackfillGroovesCouplings
CableDepth control*Poor storageAging
ProbeBias shift*Rotation*ConnectorsWheels
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Bias-Shift Error
Example 1 Example 2
Bias Shift and Checksums
Displacement Checksums
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Bias-Shift Analysis in DMM
-6.625 – -1.3
Bias-Shift Analysis in DMM
1. Display graph.
2. Check box toInclude Biasshift.
3. Choose zone.
4. Click Report.
Generate Report
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Rotation Error & Cross-Axis Profile
Displacement A Casing Profile B
Example 1
Factor = Displacement Error AProfile B
Displacement Error A = 35 mmProfile B = 4500 mm
Factor = 354500
= 0.0078
Calculating a Correction Factor
Displacement A Profile B
35 4500
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Calculating a Correction Factor
35 mm
4500 mm
B0
A0
Correction = Displacement Error AProfile B
= 35 mm4500 mm
= 0.0078
Correction value is the sine of the angleof rotation and is normally < 0.0175 ( sin 1° ).
Probe is lower if …• Casing was cut off.• Use of pulley halted.• Casing settled.• Cable lengthened.
Probe is higher if …• Casing was added.• Use of pulley started.• Cable twisted.• Cable shortened.
Probe Position: High or Low?
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Depth Error
Example 1
Curvature Displacement
Curvature vs Displacement
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Curvature vs DisplacementExample 2
Curvature Displacement
Curvature Displacement
Curvature vs DisplacementExample 2
Scale changed
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Depth Error in S-Shaped Casing
Curvature Displacement Curvature Displacement
Low High
Depth Error in J-Shaped CasingLow High
Curvature Displacement Curvature Displacement
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Depth Correction in DMM
PotentialSystematicError