Post on 26-Mar-2015
ASTM 2011 Workshop JTG.1
A Perspective on Geotechnical Testing:
The Details Matter
John T. Germaine
Massachusetts Institute of TechnologyDepartment 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 TestsLaboratory A Laboratory CLaboratory B
Total Index
Strength
Compaction
Hydraulic Cond.
Consolidation
Laboratory D
• Very informal poll• Three large commercial• One in-house engineering• Test numbers, not revenue
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Distribution Minus IndexLaboratory A Laboratory B Laboratory C Laboratory D
Compaction
Hydraulic Cond.
Consolidation
Simple Strength
Other Strength
• 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
• Formal Standards• ASTM• AASHTO• BS
• In-house procedures
• Facilitate communication
• Product uniformity
• Solidify professional practice
• Expand domain of expertise
• 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
• 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
• 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
• <20067 %
• < 2m29 %
• Gs 2.644• LL
29 • PI 13• USCS
CL
• Sample 158
• <200 62 %• < 2m 27 %• Gs 2.645• LL 28 • PI 13• USCS CL
2008 Proficiency Testing Program
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Specific Gravity Results
2.0
2.2
2.4
2.6
2.8
3.0
3.2
2.0 2.2 2.4 2.6 2.8 3.0 3.2
Specific Gravity of Sample 158, (gm/cm3)
Sp
eci
fic
Gra
vit
y o
f S
am
ple
157, (g
m/c
m3)
• Huge range in results
• Within laboratory correlation
• Systematic error in procedure
• 1995 study same variability
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Specific Gravity Results
0
10
20
30
40
50
60
70
2.50 2.55 2.60 2.65 2.70 2.75
Sample 157
Sample 158
Specific Gravity, (gm/cm3)
Num
ber
of
Obse
rvati
on
s
• Eliminate outliers
• Wide distribution
• Bias towards low values
• Useful range 0.01
• ASTM• Repeatability
• 0.02
• Reproducibility• 0.06
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Example: Shrinkage Limit Test
• 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 89 / 83 %
– < 2m 39 / 37 %
– Gs 2.704 / 2.699
– LL43.0 / 43.2
– PI 20.8 / 20.9
– USCS CL
• Sample 161 / 162
– <200 65 / 46 %– < 2m 24 / 20 %– Gs 2.733 /2.694
– LL 24.8 / 23.7 – PI 10.2 / 10.1– USCS 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
• AMRL proficiency program• Method: ASTM D698• Samples 157 and 158• 963 Laboratories• Report only wopt and gmax
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Compaction Results
6
8
10
12
14
16
18
20
22
6 8 10 12 14 16 18 20 22
100
105
110
115
120
125
130
100 105 110 115 120 125 130
157 Max. Dry Unit Weight, lbf/ft315
8 M
ax.
Dry
Unit
Weig
ht,
lbf/
ft3
157 Opt. Water Content, %
15
8 O
pt.
Wate
r C
onte
nt,
% • Water Content• Weak correlation• Processing issues• 157 higher• Serious outliers
• Unit Weight• Better correlation• Technique differences• 157 lower
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Compaction Results
0
10
20
30
40
50
60
70
80
9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 13.0
Sample 157
Sample 158
0
20
40
60
80
100
120
140
116 118 120 122 124 126 128
Sample 157
Sample 158
Max. Dry Unit Weight, lbf/ft3
Opt. Water Content, %
Num
ber
of
Obse
rvati
on
sN
um
ber
of
Obse
rvati
on
s
• Outliers Removed
• Water Content• Broad distribution• Subtle difference
• Unit Weight• Narrow center band• Clear shift in average• Symmetrical tails
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100
105
110
115
120
125
130
5 7 9 11 13 15 17 19
158 Measured data
100
105
110
115
120
125
130
5 7 9 11 13 15 17 19
158 Measured data
One lab with curve
100
105
110
115
120
125
130
5 7 9 11 13 15 17 19
158 Measured data
One lab with curve
Zero air voids
Compaction Results
• Considerable scatter
• Clear outliers• No trend• Unlikely results• Impossible results
Water Content, %
Dry
Uni
t Wei
ght,
lbf/
ft3
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Compaction Results
100
105
110
115
120
125
130
5 7 9 11 13 15 17 19
Dry
Uni
t Wei
ght,
lbf/
ft3
Water Content, %
• wopt =10.7 %
• gmax =122.6 lbf/ft3
AMRL Proficiency Sample 158
• Field specification• +/- 2 % wc
• 92 % R.C.
• Field specification• Including 2 Std.
Dev.
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lll: Hydraulic Conductivity
• 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
• 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• CH
Sample− <200 96
%− < 2 m
46 %− LL 60− PI 39− USCS CH− Vicksburg
clay
• ML Sample
– <200 99 %– < 2 m 8
%– LL 27 – PI 4– USCS ML– Vicksburg silt
• CL Sample
− <200 89 %− < 2 m
31 %− LL 33 − PI 14− USCS CL− Annapolis
clayASTM ISR managed 15,000 lbs of each soilNSF, FHWA, and private sponsorship Started 1993
7 Precision statements
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0.0
0.5
1.0
1.5
2.0
2.5
3.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Individual testML Lab average
Average +/- Std DevLog Ave +/- Std Dev
Hydraulic Conductivity Results
Laboratory Number
Hyd
raul
ic C
ondu
ctiv
ity,
(cm
/s)
(10-6
) • Variable Scatter with in labs
• Two outlier labs
• Some labs very consistent
• Log std. dev. fairly good
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0
5
10
15
20
25
30
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Hydraulic Conductivity Results
0.0
1.0
2.0
3.0
4.0
5.0
6.00.0
0.5
1.0
1.5
2.0
2.5
3.0Individual test
ML Lab average
Average +/- Std Dev
Log Ave +/- Std Dev
Laboratory Number
Hydra
ulic
Cond
uct
ivit
y,
cm/s
• ML (x10-6) natural log• 1.2 1.1• 0.8-1.6 0.8-
1.5
• CL (x10-8)• 3.8 3.7• 3.2-4.4 3.2-
4.4
• CH (x10-9)• 3.6 2.6• <0-8.2 1.3-
5.2
Avg.
S. D.
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Hydraulic Conductivity Results
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1 2 3 4 5 6 7 8 9 10 11 12 13 14
Laboratory Number
Hyd
raul
ic C
ondu
ctiv
ity,
(cm
/s)
1.E-09
1.E-07
1.E-05
1234567891011121314
Laboratory Number
Individual test
ML Lab average
CL Lab average
CH Lab average
Average +/- Std Dev
Log Ave +/- STD Dev
Individual test
Average +/- Std Dev
Log Ave +/- STD Dev
Individual test
Average +/- Std Dev
Log Ave +/- STD Dev
• Log provides better representation
• Equip. tuned to 10-
7
• < one sign. digit
• Real problems for low permeability
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lV: Consolidation and Shear• 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• 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• 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