astm 2011 workshopjtg.1 a perspective on geotechnical testing: the details matter john t. germaine...

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


The Question

How well are we doing as a profession with regards to the characterization of soils?


Outline• Overview of soil testing

industry• Establishing quality control• Some example industry data

• Specific gravity• Shrinkage limit• Compaction• Hydraulic conductivity

• Conclusions and recommendations


Laboratory Testing Goals

• Diversity in test type

• Broad range of materials

• Accurate results

• Timely delivery

• Profitability


Testing Considerations• Test methods

• Index Tests• Engineering Tests

• No correct answer• Extreme variability of

natural materials• Huge range in results• Quality control

concerns


Testing Organizations

• Commercial companies• About 1200

• Commercial laboratories

• In-house engineering consultants

• Small independent laboratories

• Government organizations• About 110

• Academic research laboratories• About 180


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


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


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


Documented Protocols

• Formal Standards• ASTM• AASHTO• BS

• In-house procedures

• Facilitate communication

• Product uniformity

• Solidify professional practice

• Expand domain of expertise

• Improve product quality


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


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


l: Classification and Index

• Simple equipment• Considerable labor• Technical skill and finesse• Difficult to check results• Rely on consistency and

correlations


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


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


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


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


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


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


Shrinkage Limit: Wax Method

• Huge range in results




Shrinkage Limit: Wax Method

• Wide distribution

• Second year improvement

• Distribution skewed to higher values


Shrinkage Limit: Hg Method

• About the same range as Wax method




Shrinkage Limit: Hg Method

• Clear difference between each year

• Most labs in narrow range

• Serious outliers


Shrinkage Limit: Summary

• Wax gives lower values• Wax method has more scatter• Average values capture subtle

differences


ll: Laboratory Compaction• Simple equipment

• Calibration of automatic hammers• Energy transfer

• Material processing very important• Technical skill• Interpretation of results


Example: Standard Proctor

• AMRL proficiency program• Method: ASTM D698• Samples 157 and 158• 963 Laboratories• Report only wopt and gmax


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


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


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


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.


lll: Hydraulic Conductivity

• Widest range of any parameter

• Extreme equipment demands• Little automation• Expertise more than finesse• Attention to detail• QC equipment


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


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


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


0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10 11 12 13 14


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.



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


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


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


Recommendations• Formal protocols for every test• Technician training• Consistency evaluation of results• Reference material testing• In-house databases• Participation in ASTM


Acknowledgements

• Friends associated with ASTM• Ron Holsinger; AMRL• Craig Benson; U of Wisconsin

astm 2011 workshopjtg.1 a perspective on geotechnical testing: the details matter john t. germaine...

Documents

astm d854 method

product quality slide

revenue slide

geotechnical testing

collective test results

test method precision

test method d18 standards

test type diversity