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A Perspective on Geotechnical Testing: The Details Matter

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Presentation on theme: "A Perspective on Geotechnical Testing: The Details Matter"— Presentation transcript:

1 A Perspective on Geotechnical Testing: The Details Matter
John T. Germaine Massachusetts Institute of Technology Department of Civil and Environmental Engineering ASTM 2011 Workshop

2 The Question How well are we doing as a profession with regards to the characterization of soils? ASTM 2011 Workshop

3 Outline Overview of soil testing industry Establishing quality control
Some example industry data Specific gravity Shrinkage limit Compaction Hydraulic conductivity Conclusions and recommendations ASTM 2011 Workshop

4 Laboratory Testing Goals
Diversity in test type Broad range of materials Accurate results Timely delivery Profitability ASTM 2011 Workshop

5 Testing Considerations
Test methods Index Tests Engineering Tests No correct answer Extreme variability of natural materials Huge range in results Quality control concerns ASTM 2011 Workshop

6 Testing Organizations
Commercial companies About 1200 Commercial laboratories In-house engineering consultants Small independent laboratories Government organizations About 110 Academic research laboratories About 180 ASTM 2011 Workshop

7 Distribution of Tests Very informal poll Three large commercial
One in-house engineering Test numbers, not revenue ASTM 2011 Workshop

8 Distribution Minus Index
Significantly different distributions Large number of strength tests In-house QC type testing ASTM 2011 Workshop

9 Quality Control Tools ISO Certification ASTM D3740 NICET
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 ASTM 2011 Workshop

10 Documented Protocols Facilitate communication Product uniformity
Solidify professional practice Expand domain of expertise Improve product quality Formal Standards ASTM AASHTO BS In-house procedures ASTM 2011 Workshop

11 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 ASTM 2011 Workshop

12 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 ASTM 2011 Workshop

13 l: Classification and Index
Simple equipment Considerable labor Technical skill and finesse Difficult to check results Rely on consistency and correlations ASTM 2011 Workshop

14 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 ASTM 2011 Workshop

15 AMRL Sample Specifics Sample 157 Sample 158 <200 67 % < 2m 29 %
< % < 2m 29 % Gs 2.644 LL 29 PI 13 USCS CL Sample 158 < % < 2m 27 % Gs 2.645 LL 28 PI 13 USCS CL 2008 Proficiency Testing Program ASTM 2011 Workshop

16 Specific Gravity Results
Huge range in results Within laboratory correlation Systematic error in procedure 1995 study same variability Specific Gravity of Sample 157, (gm/cm3) Specific Gravity of Sample 158, (gm/cm3) ASTM 2011 Workshop

17 Specific Gravity Results
Eliminate outliers Wide distribution Bias towards low values Number of Observations Useful range 0.01 ASTM Repeatability 0.02 Reproducibility 0.06 Specific Gravity, (gm/cm3) ASTM 2011 Workshop

18 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 ASTM 2011 Workshop

19 AMRL Sample Specifics Sample 159 / 160 Sample 161 / 162
< / 83 % < 2m 39 / 37 % Gs / 2.699 LL 43.0 / 43.2 PI 20.8 / 20.9 USCS CL Sample 161 / 162 < / 46 % < 2m 24 / 20 % Gs /2.694 LL 24.8 / 23.7 PI 10.2 / 10.1 USCS CL 2009 & 2010 Proficiency Testing Program ASTM 2011 Workshop

20 Shrinkage Limit: Wax Method
Huge range in results Within laboratory correlation Systematic error in procedure ASTM 2011 Workshop

21 Shrinkage Limit: Wax Method
Wide distribution Second year improvement Distribution skewed to higher values ASTM 2011 Workshop

22 Shrinkage Limit: Hg Method
About the same range as Wax method Within laboratory correlation Systematic error in procedure ASTM 2011 Workshop

23 Shrinkage Limit: Hg Method
Clear difference between each year Most labs in narrow range Serious outliers ASTM 2011 Workshop

24 Shrinkage Limit: Summary
Wax gives lower values Wax method has more scatter Average values capture subtle differences ASTM 2011 Workshop

25 ll: Laboratory Compaction
Simple equipment Calibration of automatic hammers Energy transfer Material processing very important Technical skill Interpretation of results ASTM 2011 Workshop

26 Example: Standard Proctor
AMRL proficiency program Method: ASTM D698 Samples 157 and 158 963 Laboratories Report only wopt and gmax ASTM 2011 Workshop

27 Compaction Results Water Content Unit Weight Weak correlation
Processing issues 157 higher Serious outliers Unit Weight Better correlation Technique differences 157 lower 158 Opt. Water Content, % 157 Opt. Water Content, % 158 Max. Dry Unit Weight, lbf/ft3 157 Max. Dry Unit Weight, lbf/ft3 ASTM 2011 Workshop

28 Compaction Results Outliers Removed Water Content Unit Weight
Broad distribution Subtle difference Unit Weight Narrow center band Clear shift in average Symmetrical tails Number of Observations Opt. Water Content, % Number of Observations Max. Dry Unit Weight, lbf/ft3 ASTM 2011 Workshop

29 Compaction Results Considerable scatter Clear outliers No trend
Dry Unit Weight, lbf/ft3 Unlikely results Impossible results Water Content, % ASTM 2011 Workshop

30 Compaction Results wopt =10.7 % gmax =122.6 lbf/ft3
Field specification +/- 2 % wc 92 % R.C. Dry Unit Weight, lbf/ft3 Field specification Including 2 Std. Dev. Water Content, % AMRL Proficiency Sample 158 ASTM 2011 Workshop

31 lll: Hydraulic Conductivity
Widest range of any parameter Extreme equipment demands Little automation Expertise more than finesse Attention to detail QC equipment ASTM 2011 Workshop

32 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 ASTM 2011 Workshop

33 ISR Sample Specifics ML Sample CL Sample CH Sample <200 99 %
< % < 2m % LL PI USCS ML Vicksburg silt CL Sample < % < 2m % LL PI USCS CL Annapolis clay CH Sample < % < 2m % LL PI USCS CH Vicksburg clay ASTM ISR managed ,000 lbs of each soil NSF, FHWA, and private sponsorship Started 1993 7 Precision statements ASTM 2011 Workshop

34 Hydraulic Conductivity Results
Variable Scatter with in labs Two outlier labs Some labs very consistent Log std. dev. fairly good Hydraulic Conductivity, (cm/s) (10-6) Laboratory Number ASTM 2011 Workshop

35 Hydraulic Conductivity Results
ML (x10-6) natural log CL (x10-8) CH (x10-9) < Avg. S. D. Hydraulic Conductivity, cm/s Laboratory Number ASTM 2011 Workshop

36 Hydraulic Conductivity Results
Log provides better representation Equip. tuned to 10-7 < one sign. digit Real problems for low permeability Hydraulic Conductivity, (cm/s) Laboratory Number ASTM 2011 Workshop

37 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 ASTM 2011 Workshop

38 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 ASTM 2011 Workshop

39 Recommendations Formal protocols for every test Technician training
Consistency evaluation of results Reference material testing In-house databases Participation in ASTM ASTM 2011 Workshop

40 Acknowledgements Friends associated with ASTM Ron Holsinger; AMRL
Craig Benson; U of Wisconsin ASTM 2011 Workshop

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