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.
3
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
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