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Technical Note (National Research Council of Canada. Division of Building Research), 1972-05-19
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Reliability of Soil Classification Test Techniques
Eden, W. J.
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DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
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JH[
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NOTE
No.
565
PREPARED BY W.J. Eden
PREPARED FOR Record purposes
CHECKED BY LWG APPROVED BY CBC DATE May 19. 1972 SUBJECT
RELIABILITY OF SOIL CLASSIFICATION TEST TECHNIQUES
In 1964 the American Council of Independent Laboratories (ACIL) in cooperation with Committee D-18 of the AmeriCan
Society for Testing and Materials (ASTM) engaged in a comparison ｴｾｳｴ program. Three standard bulk samples of high, medium and low plasticity were carefully mixed and sent to any laboratory wishing to take part in the program. Each participating laboratory conducted the following tests according to ASTM procedure: Liquid Limit (D423-61 T). Plastic Limit (D424-59), Grain Size (D422-63), Specific Gravity (D854-58), Standard Moisture/Density Relation (D698-58T) and Modified Moisture/Density Relation (D1557-50T).
More than 200 laboratories took part in the program, the Soil Mechanics Laboratory of the Division of Building Research being one of them. and results were duly reported to Committee D-18 for study. Serious discrepancies were indicated in the results from different laboratories. Since most of the samples treated by the Soil Mechanics Laboratory were undisturbed clays at natural water contents, the testing procedures differ in some detail from the standCl,rd ASTM procedures. In order to assess the reliability of the soil classification tests carried out routinely in the laboratory, three specially prepared samples were subjected to a series of
-2-classification tests by three different well qualified technicians. Two sample blocks from the Ottawa sewage treatment plant and one from the floodway excavation in Winnipeg were chosen. After mixing, each was split in three and subjected to the following tests: water ｣ｯｮｴ･ｮｴｾ
ｦ｡ｬｬＭ｣ｯｮ･ｾ Atterberg ｌｩｭｩｴｳｾ grain size. specific gravity and shrink-age factors.
TEST METHOD
The blocks, weighing about 3000 grams ･｡｣ｨｾ were thoroughly remoulded with a mechanical mixer, split into three portions of about 1000 gm and labelled 1, 2, 3. Each of the nine sub-samples was then subjected to the classification tests following the procedure listed in the laboratory manual. Sample X was a medium high plastic clay and designated X-I, X-2 and X-3. Y was an extremely sensitive clay of medium plasticity and designated YＭｬｾ Y -2 and Y -3. Z was a highly plastic insensitive clay and designated Z-l, Z-2 and Z-3; it was necessary to add water to sample Z to mix it thoroughly.
X-I, Y -1 and Z -1 were assigned to Technician 1 for testing; X-2, Y-2 and Z-2 to Technician 2; and X-3, Y-3 and Z-3 to Tech-nician 3. The technicians were aware that some of the samples were duplicated, but did not know the significance of the sample designations. They were asked to conduct the tests with no more than the usual care generally exercised with routine test work.
TEST RESULTS
The results are presented in Table I. They reveal no serious discrepancies. They also indicate that the personal factor in results of tests carried out with reasonable care is not serious. For example, with the liquid limit test, Technician 1 had two test results less than average and one above average.
The liquid limit seemed to be one of the more accurate tests. The percentage error for sample X was 3. 4, for Y 4. 7 and for Z 1.6. Sample Y was the least ｡｣｣ｵｲ｡ｴ･ｾ probably because it exhibited a tendency to gel very quickly, a fairly common feature of extremely sensitive clays. The tendency to gel also shows up in the remoulded cone readings for sample Y.
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-3-The grain size tests gave reasonably good agreement. The grain size curves show only one test of the nine to be questionable. It is believed that the error in this test may have occurred when the sample was weighed.
Surprisingly good agreement was achieved with shrinkage factor tests in spite of a rather complicated test procedure. This test is rarely conducted by the technicians in question and in this case it may be stated that they were not experienced.
The remoulded cone gave very good results for two of the samples; sensitive clay cone determinations were influenced by the tendency of the sample to gel.
CONCLUSIONS
Routine laboratory procedures have proved reliable. Results of such tests appear to have about equal accuracy (± 3 per cent) and should therefore be reported to the nearest whole number, as recom-mended in a number of standard procedures, except for specific
gravity and shrinkage ratio.
There does not appear to be any significant personal factor in the results of the comparison tests carried out.
ACKNOWLEDGEMENT
The assistance of L. Boyd, A. Guibord, D. MacMillan and K. Timmins is gratefully acknowledged in preparing samples and conducting the tests.
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TABLE I
SUMMARY OF TEST RESULTS
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SAMPLE X SAMPLE Y SAMPLE Z TECHNICIAN 1 2 3 Av 1 2 3 Av 1 2 3 Av Water Content 68.2 68.5 67.4 68.0 52.2 52. 1 51. 8 52.0 82.2 82.0 80.8 81. 7 (0. 9) (0. 4) (1. 1) Liquid Limit 50.6 53. 1 53.5 52.4 37.6 40.4 37.8 38.6 82.6 80. 1 81.6 81. 4 (3. 4) (4. 7) (1. 6) Plastic Limit 25.6 25.6 25.2 25. 5 24.3 26.8 24.7 25.3 30.2 30.0 29.7 30.0 (1.2) (5.9) (1.0) Plasticity Ind ex 25.0 27.5 28.3 26.9 13. 3 13. 6 13. 1 13. 3 52.4 50. 1 51. 9 51.4 (7.0) (2.3) (2. 5) Shrinkage Limit 19.8 20.9 20. 1 20.3 18.4 20.9 19. 2 19.5 15.6 15.8 14.9 15. 1 (2.9) (7.2) (4.6) Shrinkage Ratio 1. 80 1. 76 1. 76 1. 77 1.81 1.74 1. 77 1.
