GeoGaugeTM LectureSeptember 2001

Scott FiedlerProduct Manager

Humboldt Mfg. Co., Norridge, Illinois U.S.A.

2

GeoGaugeTM

• Directly measures the in-situ or in-place stiffness.

• Manufactured by Humboldt Mfg. Co. in Norridge, Illinois U.S.A.

• U.S.A. and World Patent Pending

• GeoGauge is trademark of Humboldt Mfg. Co.

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Why The GeoGauge?•• To Meet A NeedTo Meet A Need

•• Relentless Pursuit of Lower Cost & Higher QualityRelentless Pursuit of Lower Cost & Higher Quality•• By Achieving A GoalBy Achieving A Goal

•• Increased Precision of Design & ConstructionIncreased Precision of Design & Construction•• Mechanistic DesignsMechanistic Designs•• Performance SpecificationsPerformance Specifications•• Process ControlProcess Control

•• Increased Continuity Between Design & ConstructionIncreased Continuity Between Design & Construction•• Design Parameters Used to Evaluate ConstructionDesign Parameters Used to Evaluate Construction•• Contractor WarrantiesContractor Warranties

•• Through A Historically Successful PathThrough A Historically Successful Path•• Structural Stiffness & Material ModulusStructural Stiffness & Material Modulus

•• Engineering / Mechanistic ValuesEngineering / Mechanistic Values

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Physical Attributes• Size: 280mm diameter x

255mm tall• 114mm OD x 89mm ID

Ring Foot• Weight: 10 kg• Powered by 6 D-Cell

Batteries• IR Data Downloading

(Optional)• Keypad User Interface

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Operating Principle

• At GeoGauge Frequencies & Stress, Impedance is Predominately Stiffness

• No Need for a Non-Moving Displacement Reference• Permits the Accurate Measurement of Small Displacements

Stiffness

Modulus

= Resistance of a Layer or Structure to Deformation

= Resistance of a Material to Deformation

+ Foot Radius&

Poisson’s Ratio

Fdr = Kflex (X2 - X1)

Kgr = Fdr

X1

Kgr = K flex Σ 1

n(X2 - X1)

X 1 Σ 1

n(V2 - V1)

V1

= Kflex

n n

1int2

12flexdr Xmù)X(XKF +−=

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Measurement Procedure• Inspect GeoGauge• Power On• Select Mode & Poisson’s Ratio• Seat the Foot

• > 60% Direct Contact• Moist Sand Assisted (3 to 6 mm thick)

• Rough & Irregular Surfaces• Smooth Hard Surfaces

• Take the Measurement:• 75 Seconds (15 sec. Noise + 60 sec. Signal)• Results Displayed

• Signal/Noise: > 3/1 (10 db)• Standard Deviation: a Measure of Foot Contact• Average Stiffness or Modulus (English or SI)

• Examine the Foot Print• Save Data

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Specification• Stiffness: 3 to >70 MN/m (17 to >399 klbf/in)

• Young’s Modulus: 26 to >607 MPa (4 to >88 kpsi)

• Poisson’s Ratio: 0.20 to 0.70 in 0.05 Increments

• Precision: Typically 3.9% Coefficient of Variation

• Bias: < 1% Coefficient of Variation

• Depth of Measurement: 220 to 310 mm

• Battery Life: > 1,500 measurements

• Operating Temperature: 0 to 38°C

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Precision

• Typical Coefficient Of Variation: 3.9%• Basis: 3 Gauges, 3 Operators & 470 Measurements

Single GaugeDate Site Material

Mean 1σσ Mean 65% Confidence

95% Confidence

8/16/96 Salisbury ByPass Silty Sand 6.28 0.28 4.08 6.01 7.94

9/19/96 NM 44 Sandy Clay Subgrade* 11.33 0.37 3.31 - -

10/12/96 16 Vegas Dr. Sility Clay** 8.86 0.47 5.35 7.17 9.00

10/13/96 16 Vegas Dr. Full Depth Pavement* 51.37 2.17 4.25 5.66 7.07

10/19/96 I70/ I270 Graded GAB* 40.20 1.57 3.84 5.21 6.58

10/28/96 Rutters Fat Clay* 12.74 0.35 2.67 3.13 3.59

* Assisted Seating (moist sand)** Unprepared ground

Coeff. Of Var., %Typical Stiffness, MN/ m

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Date Site Material No. of Measurements Coeff. of Var.Mean 1σσ %

11/6/96 16 Vegas Dr. Sility Clay** 12 8.50 0.33 3.89

11/6/96 16 Vegas Dr. Sility Clay** 30 9.94 0.39 3.91

11/7/96 16 Vegas Dr. Full Depth Pavement* 16 44.83 1.72 3.83

11/23/96 16 Vegas Dr. Sility Clay** 10 10.06 0.59 5.84

* Assisted Seating (moist sand)** Unprepared ground

Stiffness, MN/ m

Precision

• Statistics Based on Combined Measurements From Both Gauges• Basis: 2 Gauges, 1 Operator & 68 Measurements

Multiple Gauges

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Bias • Reference: Moving Mass

• Known Mass: 10 kg • 25 Known Frequencies: 100 to 196 Hz • Stiffness = -jωω2M

• Coefficient of variation: < 1%

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Calibration Platen• Reference: Moving Mass, Platen of Certain Geometry

• Known Mass: 10 kg • 25 Known Frequencies: 100 to 196 Hz • Stiffness = -jωω2M

• Coefficient of variation: < 1%

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Verifier Mass

• Used whenever a check of GeoGauge operation is desired

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What is GeoGauge Stiffness ?Quasi-Static Field Plate Load Test Results

0

10

20

30

40

50

60

0 0.005 0.01 0.015 0.02 0.025 0.03

k=1.68

k=12.8 klb/in

k=11.8

k=14.8

k=14.7

k=18.2

k=6.98

k=8.01

k=8.15

GeoGauge Measurement: k=14.5 klb/in

Unloading

Loading

Deflection, (in)

Load(lb)

GeoGauge Measures the Reaction of the Soil to Removing the Working

Load

Performed byCNA Consulting Engineers

Typ. of a Granular BaseSeptember, ‘99

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• Model Footing Precisely Constructed of Cohesionless Sand• Measure Stiffness With GeoGauge• Calculate 9‘ Layer Stiffness From:

• Measured Void Ratio• Estimated Mean Effective Stress

Under GeoGauge Foot• Estimated Poisson’s Ratio

• Measured Stiffness Within 5% of Calculated Value

• GeoGauge Can Sense BoundariesUp to 12” From Its Foot

• To be Repeated on Silt, Clay & Layered Media

GeoGauge Stiffness: How To Confirm It?GeoGauge Stiffness: How To Confirm It?

Uniform Vertical Annular Line LoadCenter Line Stress @ r = 0(Line Load = 1.752 lb/in.,

Annular Radius, a = 2.0 in.)

0

3

6

9

12

15

18

21

24

0.00 0.40 0.80 1.20 1.60

Vertical Effective Stress, psi

Dep

th, i

n.

Geostatic Effective StressLoad Induced StressTotal Stress

University of New Mexico, ATR Institute

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Correlation to Other Moduli

0

300

600

900

1200

1500

0 50 100 150 200 250 300 350 400

0

500

1000

1500

2000

2500

0 50 100 150 200 250 300 350 400

-50

0

50

100

150

200

1 2 3 4 5 6

95

100

105

110

115

120

PFWD (small plate)

PFWD (large plate)

DCP (6" avg.)

DCP (3" avg.)

GeoGauge

sc compaction

ng compaction

Section 17, Mn/ROAD

13 Pavement Sectionsat 5 MnDOT Sites

Modulus(MPa)

Compaction(%)

Subgrade & Base MaterialsIn 6 TXDOT Districts

GeoGauge, EG, (MPa)

EF = 4.08EG - 231.53Correlation Coefficient: .80

FWD vs. GeoGauge Modulus

FWD, EF

(MPa)GeoGauge, EG, (MPa)

Seismic vs. GeoGauge Modulus

ES = 6.27EG - 31.91Correlation Coefficient: .79

Seismic, ES

(MPa)

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Correlation to Dry Density

85

90

95

100

105

110

85 90 95 100 105 110 115

0

1000

2000

3000

4000

5000

0 500 1000 1500 2000

K/m^.25, kip/ft

ρ 0

1 + 1.2 [ - .3].5mCK

.5

Analytical-Empirical Relationship

C = (K/m){[(ρ 0/ρ D-1)/1.2] + 0.3}2

Calculate C From Regional CompanionMeasurements of Stiffness, Moisture Content

& Dry Density

Define Several Linear RelationshipsBetween C and K/m .25 For

Groups of Regional Soil Classes

From Measurements of Stiffness &Moisture Content And A Calculated C,

Estimate Dry Density Using the SameAnalytical-Empirical Relationship

A-2-4 and A-2-5 Soils

C = 2.26(K/m .25 ) + 160.36Correlation Coefficient: 0.98

Estimated DensityRe

Measured Density

ρρ (GeoGauge), pcf

ρρ (Nuclear), pcf

A-2-4 and A-2-5 Soils

ρρ (GeoGauge.) = 0.58( ρρ (Nuc )) + 39.39

Correlation Coefficient: 0.78

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11

33

44

Data from MODOT,November, ‘99

C, klb/in

K/m .25, klb/in

C, klb/in

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Other Correlations• Resilient Modulus• Unconfined Compressive Strength• California Bearing Ratio (CBR)• Dynamic Cone Penetrometer (DCP)• Static Cone Penetrometer• Plate Load

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GeoGauge Alternatives

Metho d:In-Place

Sti ffness orMod ulu s

Sp

*Production Test: One that does not delay or interfere with construction

*

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Development: BBN Shallow Soil Seismic/Acoustic Research

• Soil Physics & Measurements• Soil Impedance• Wave Propagation

• Transducer Coupling Research

• System Development & Displays

Hole

Mine

Seis

mic

Arr

ay

2 m

Seismic Sonar Display of Response of Mine

BBN Proprietary Weight-biasedGeophones and Compact Vibrator Source

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Design Validation• Alpha

• Field Trials: MN, NY & TX• Construction Noise: Freq. Shift & Improved Filtering• Calibration: Soil vs. Elastomer vs. Mass• Relationship Between Density & Modulus

• Beta• Field Trials: MN, TX, NC, FL, OH, CA, NJ & MO• Usability & Reliability• Manufacturing & Test Methods Development• Establish Precision & Bias

• Standards Development• ASTM• AASHTO

Benefits ofStiffness & Modulus Today

•Control of Compaction•Mitigating the Risk of Pavement Failure•Control of Stabilized Fill Quality

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Control of Compaction Quality

• Job by Job / Material by Material Evaluation

• Stiffness added to Proctor or Proctor Like Testing

• Empirical Relationship vs. Moisture Determined

• “Unique” Stiffness of each Moisture & Density Pair

• Stiffness Lab / Test Strip Correction (Proctor Mold)

• Conditions for Using Stiffness• Lift Thickness: > 8”• Awareness of Variability

from Lift Support

Density or Stiffness

106

108

110

112

114

116

118

0 5 10 15

Moisture Content, %

0

5

10

15

20

25

30

Univ. of NM, ATR Inst.Silty SandUnified SM

AASHTO A-2-4Standard Proctor Effort

Stiffness

Density

98 % Compaction

100 % Compaction

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Control of the Compaction Process• Compaction of A Layer Is Only As Good As the Supporting Material Will Allow• Directly Measure Compaction (Rate of Increase in Stiffness) As a Function of Effort• When the Rate Is Approx. Constant, the Compaction Is Optimized• ~ �30% Reduction in Compactive Effort Possible

y = 2.0739Ln(x) + 5.1028R2 = 0.9892

3

4

5

6

7

8

9

10

0 2 4 6 8

Number of Roller Passes

y = 69.379x -1.3039

R2 = 0.7217

0

10

20

30

40

50

60

70

80

0 2 4 6 8

Number of Roller Passes

Compaction of 2” of HMA

Mangum Asphalt, Inc.

June, 2000

Optimum Compaction With Minimum Effort

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Filled Trench

Pipe

Data

0

5

10

15

20

25

A B C D E F G H ILocation

UndisturbedRoadbed

BackfilledTrenchMo

du

lus

(kp

si)

Mitigating the Risk of Pavement Failure

• Sharp Stiffness Changes = Near Term Failures• Experience Is Indicating:

• + 50% Stiffness Tolerance, Fewer Near Term Failures• + 25% Stiffness Tolerance, Fewer Long Term Failures

More Uniform Stiffness = More Time Between FailuresMore Uniform Stiffness = More Time Between Failures

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Control of Stabilized Fill Quality• “Is the Fill Hard Enough?”• “Has Rain Inhibited Stabilization?”• “Can I Customize Stabilization?”• GeoGauge Can Enable:

• Monitoring of Material Cure Rate• Direct Measurement of Material

Modulus• Laboratory Design of Custom Mixes

& Determination of Indexes for Evaluating Construction

• GeoGauge Specified By USAF for Runway Infield Stabilization• Used to Estimate Increases in CBR

y = 34.975Ln(x) - 5.7668

R2 = 0.9827

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

130

1 11 21 31

Day #

2 Week s Old St ab ilized , 9 /2 0, St a. 5 0 50

2 Day Old St ab ilized , 9 /2 0, St a. 5 0 45

1 Day Old St ab ilized , 9 /2 0, St a. 5 0 45

Unst abilize d, 9 /2 0, St a. 4 8 15

St iffne ss

DryDe nsi ty

Dist ance o f~ 1 3 Miles

Evaluation of Stabilization

Rehabilitated Sandy Clay SubgradeStabilized with Lime

New Mexico Route. 44, September, ’00Koch Performance Roads

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Other Applications• Specification Development• Mechanistic Design Validation• Buried Structures QC• Utility Back-Fills QC• Determination of HMA “Tender Zone”• Evaluation of Controlled Low Strength Materials• Quantification of Soil-Cement Micro-Cracking• Cold Mix Asphalt QC