A Perspective on
Geotechnical Testing:
The Details Matter
John T. Germaine
Massachusetts Institute of Technology
Department of Civil and Environmental Engineering
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The Question
How well are we doing as a profession
with regards to the characterization of
soils?
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Outline
• Overview of soil testing industry
• Establishing quality control
• Some example industry data
•
•
•
•
Specific gravity
Shrinkage limit
Compaction
Hydraulic conductivity
• Conclusions and recommendations
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Laboratory Testing Goals
• Diversity in test type
• Broad range of
materials
• Accurate results
• Timely delivery
• Profitability
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Testing Considerations
• Test methods
• Index Tests
• Engineering Tests
• No correct answer
• Extreme variability of
natural materials
• Huge range in results
• Quality control
concerns
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Testing Organizations
• Commercial companies
• About 1200
• Commercial laboratories
• In-house engineering consultants
• Small independent laboratories
• Government organizations
• About 110
• Academic research laboratories
• About 180
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Distribution of Tests
Laboratory B
Laboratory A
Total Index
Strength
Compaction
Hydraulic Cond.
Consolidation
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•
•
•
Laboratory C
Laboratory D
Very informal poll
Three large commercial
One in-house engineering
Test numbers, not revenue
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Distribution Minus Index
Laboratory A
Compaction
Hydraulic Cond.
Consolidation
Simple Strength
Other Strength
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Laboratory B
Laboratory C
Laboratory D
• Significantly different
distributions
• Large number of strength tests
• In-house QC type testing
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Quality Control Tools
• ISO Certification
• Management, documentation and training
• ASTM D3740
• Guidance for technical, documentation and
training requirements
• NICET
•
•
• Certifies technician capabilties
AMRL laboratory assessment
• Certifies conformance to standard
AMRL proficiency sample testing
• Sends out uniform subsamples
• Evaluates collective test results
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Documented Protocols
• Facilitate
communication
• Product uniformity
• Solidify professional
practice
• Expand domain of
expertise
• Formal Standards
• ASTM
• AASHTO
• BS
• In-house
procedures
• Improve product quality
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Quality of a Test Method
• Precision and Bias
• Bias: deviation relative to true value
• Precision: variation for given test
method
• D18 standards have no Bias!
• Quantities generally do not have a
“correct” result
• Use standard caveat statement in all
standards
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Quantifying Precision
• ASTM Standard E691
• Round Robin or Interlaboratory
• Ruggedness testing
• Impact of allowable variables
• > 6 laboratories
• Triplicate testing in each lab
• Acceptable range
• 2.8 x standard deviation
• Repeatability for single operator
• Reproducibility for between labs
• Limited to independent observations
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l: Classification and Index
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•
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•
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Simple equipment
Considerable labor
Technical skill and finesse
Difficult to check results
Rely on consistency and correlations
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Example: Specific Gravity Test
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•
AMRL proficiency program
Method: ASTM D854
542 Laboratories
Samples 157 and 158
Distributed uniform dry powder
One test on each sample
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AMRL Sample Specifics
• Sample 157
•
•
•
•
•
•
<200
< 2m
Gs
LL
PI
USCS
67 %
29 %
2.644
29
13
CL
• Sample 158
• <200
• < 2m
• Gs
• LL
• PI
• USCS
62 %
27 %
2.645
28
13
CL
2008 Proficiency Testing Program
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Specific Gravity of Sample 157, (gm/cm3)
Specific Gravity Results
3.2
3.0
2.8
2.6
2.4
2.2
2.0
2.0
2.2
2.4
2.6
2.8
3.0
3.2
• Huge range in
results
• Within laboratory
correlation
• Systematic error
in procedure
• 1995 study same
variability
Specific Gravity of Sample 158, (gm/cm3)
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Specific Gravity Results
• Eliminate outliers
• Wide distribution
• Bias towards low
values
• Useful range 0.01
• ASTM
70
Number of Observations
60
50
40
Sample 157
Sample 158
30
20
10
0
2.50
2.55
2.60
2.65
Specific Gravity, (gm/cm3)
2.70
2.75
• Repeatability
• 0.02
• Reproducibility
• 0.06
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Example: Shrinkage Limit Test
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•
•
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Comparison of Wax and Hg Method
AMRL proficiency program
Method: ASTM D4943 & D427 (old)
About 50 Laboratories
Samples 159 & 160 and 161 & 162
Distributed uniform dry powder
One test on each sample
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AMRL Sample Specifics
• Sample 159 / 160
–
–
–
–
–
–
<200
< 2m
Gs
LL
PI
USCS
89 / 83 %
39 / 37 %
2.704 / 2.699
43.0 / 43.2
20.8 / 20.9
CL
• Sample 161 / 162
–
–
–
–
–
–
<200
< 2m
Gs
LL
PI
USCS
65 / 46 %
24 / 20 %
2.733 /2.694
24.8 / 23.7
10.2 / 10.1
CL
2009 & 2010 Proficiency Testing Program
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Shrinkage Limit: Wax Method
• Huge range in
results
• Within laboratory
correlation
• Systematic error
in procedure
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Shrinkage Limit: Wax Method
• Wide distribution
• Second year
improvement
• Distribution
skewed to higher
values
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Shrinkage Limit: Hg Method
• About the same
range as Wax
method
• Within laboratory
correlation
• Systematic error
in procedure
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Shrinkage Limit: Hg Method
• Clear difference
between each
year
• Most labs in
narrow range
• Serious outliers
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Shrinkage Limit: Summary
• Wax gives lower values
• Wax method has more scatter
• Average values capture subtle differences
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ll: Laboratory Compaction
• Simple equipment
• Calibration of automatic hammers
• Energy transfer
• Material processing very important
• Technical skill
• Interpretation of results
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Example: Standard Proctor
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AMRL proficiency program
Method: ASTM D698
Samples 157 and 158
963 Laboratories
Report only wopt and gmax
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Compaction Results
158 Opt. Water Content, %
22
• Water Content
20
18
16
14
12
10
8
6
6
8
10
12
14
16
18
20
22
158 Max. Dry Unit Weight, lbf/ft3
157 Opt. Water Content, %
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•
•
•
Weak correlation
Processing issues
157 higher
Serious outliers
130
• Unit Weight
125
• Better correlation
• Technique differences
• 157 lower
120
115
110
105
100
100
105
110
115
120
157 Max. Dry Unit Weight,
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125
130
lbf/ft3
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Compaction Results
Number of Observations
80
70
Sample 157
60
Sample 158
• Outliers Removed
50
40
• Water Content
30
20
10
0
9.0
9.5
10.0
10.5
11.0
11.5
12.0
12.5
13.0
Number of Observations
Opt. Water Content, %
• Broad distribution
• Subtle difference
140
120
• Unit Weight
Sample 157
100
Sample 158
• Narrow center band
• Clear shift in average
• Symmetrical tails
80
60
40
20
0
116
118
120
122
124
126
128
Max. Dry Unit Weight, lbf/ft3
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Compaction Results
• Considerable scatter
• Clear outliers
• No trend
130
Dry Unit Weight, lbf/ft3
125
120
115
110
158Measured
Measureddata
data
158
158
Measured
data
One
lab with curve
One
curve
Zerolabairwith
voids
105
100
5
7
9
11
13
15
17
19
• Unlikely results
• Impossible results
Water Content, %
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Compaction Results
• wopt =10.7 %
• gmax =122.6 lbf/ft3
Dry Unit Weight, lbf/ft3
130
125
120
• Field specification
• +/- 2 % wc
115
110
• 92 % R.C.
105
100
5
7
9
11
13
15
17
Water Content, %
19
• Field specification
• Including 2 Std. Dev.
AMRL Proficiency Sample 158
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lll: Hydraulic Conductivity
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Widest range of any parameter
Extreme equipment demands
Little automation
Expertise more than finesse
Attention to detail
QC equipment
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Example: Establishing Precision
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ASTM D5080
Craig Benson conducted study
ISR ML, CL, and CH material
Provided compacted test specimens
12 laboratories
3 tests per laboratory
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ISR Sample Specifics
• ML Sample
• CL Sample
• CH Sample
– <200
−
−
−
−
−
−
−
−
−
−
−
−
–
–
–
–
–
99 %
< 2m
8%
LL
27
PI
4
USCS ML
Vicksburg silt
<200
89 %
< 2m
31 %
LL
33
PI
14
USCS
CL
Annapolis clay
ASTM ISR managed
NSF, FHWA, and private sponsorship
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<200
96 %
< 2m
46 %
LL
60
PI
39
USCS
CH
Vicksburg clay
15,000 lbs of each soil
Started 1993
7 Precision statements
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Hydraulic Conductivity, (cm/s) (10-6)
Hydraulic Conductivity Results
3.0
• Variable Scatter
with in labs
Individual test
ML Lab average
Average +/- Std Dev
Log Ave +/- Std Dev
2.5
2.0
• Two outlier labs
1.5
• Some labs very
consistent
1.0
0.5
0.0
1
2
3
4
5
6
7
8
9
10 11 12 13 14
Laboratory Number
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• Log std. dev. fairly
good
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Hydraulic Conductivity Results
• ML (x10-6)
3.0
Individual test
ML Lab average
2.5
Average +/- Std Dev
Log Ave +/- Std Dev
2.0
natural
Avg. • 1.2
S. D. • 0.8-1.6
Hydraulic Conductivity, cm/s
1.5
1.0
0.5
0.0
6.0
5.0
log
1.1
0.8-1.5
• CL (x10-8)
4.0
3.0
• 3.8
• 3.2-4.4
2.0
1.0
0.0
30
3.7
3.2-4.4
25
• CH (x10-9)
20
15
10
5
0
1
2
3
4
5
6
7
8
9
10
Laboratory Number
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12
13
14
• 3.6
• <0-8.2
2.6
1.3-5.2
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Hydraulic Conductivity Results
Hydraulic Conductivity, (cm/s)
1.E-05
1.E-06
• Log provides better
representation
1.E-07
• Equip. tuned to 10-7
1.E-08
• < one sign. digit
1.E-09
1 2
3 4 5 6 7 8 9 10 11 12 13 14
Laboratory Number
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• Real problems for
low permeability
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lV: Consolidation and Shear
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Significant advances in equipment
Extensive automation
Technical expertise
Sample quality and handling
Testing decisions based on soil behavior
Essentially no precision data
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Conclusions
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QC tools are available
Equipment adequate
Too much scatter
Causes of scatter are not obvious
No data for consolidation or strength
Substantial room for improvement
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Recommendations
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Formal protocols for every test
Technician training
Consistency evaluation of results
Reference material testing
In-house databases
Participation in ASTM
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Acknowledgements
• Friends associated with ASTM
• Ron Holsinger; AMRL
• Craig Benson; U of Wisconsin
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