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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