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Technical Note (National Research Council of Canada. Division of Building Research), 1955-11-01
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Trial of one-point liquid limit method
Eden, W. J.
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.
--NATIONAL RESEARCH COUNCIL OF CANADA
DIVISION OF BUILDING RESEARCH
No.
NOTlE
TEe 1HI
Ii
][
CAlL
e
206NOT FOR PUBLICATION FOR INTERNAL USE PREPARED BY iv.J. Eden CHECKED BY APPROVED BY
R.F.L.
PREPARED FOR Ninth Canadian Soil MechanicsConference, Vancouver, 1955.
November 1955.
SUBJECT
Trial of One.Point Liquid Limit Method.
There has been considerable attention devoted to the simplification of the Liquid Limit proyeoure in recent years, This was started by the U.S. Corps of ｅｮｧｩｮ･ｾｲｳｴｬＩ and extended by the U.S. Bureau of Public Roads under Olmsteadt 2 ). The simplified or one-point method consists of determining the number of blows at one water content for a soil, and by a process of extrapolation determining the liquid limit. Thus the one-point method will significantly reduce the cost of liquid limit determinations ..
Olmstead(2) has suggested that many checks on the one-point method be made by other laboratories. If such analysis leads to reasonable accuracy, then steps can be taken to adopt the one-noint method as a standard test by such bodies as tLtJ American Soc .. for :nesting Materials and American Association of state Highway Officials.
At the Eighth Canadian ｾｯｩｬ Mechanics Conference(3), the results of analyses of three Canadian soils were presented. Since then the analyses have been extended to include 390 liquid limit determinations. Most of the determinations were on soils from the Ottawa and Steep Rock Lake areas, but some test results on soils from all parts of Canada were included. The analyses were conducted by assembling the 390 determinations made by use of three or more points. From these test results, one determination at
"N"
blows was chosen and the liquid limit was calculated using the coefficient tabled later. This value of liquid limit was tabulated against the value determined by the conventional method.N
was taken anywhere between 15 and 35 blows; in most cases i t was taken between 15 and 20 or 30 and 35 blows.The maximum difference between the values of liquid limit was 6.6 per ｣･ｮｾＮ This sample contained an appreciable amount of organic material and should not have been included. 95 per cent of the 390 tests had discrepancies less than 2 per cent and
67
per cent less than 1 per cent. Thus practically all the tests, except those on organic soils fall in the 2 per cent limit set by Olmstead, in spite of the fact that values of N were deliberately cn6sen between 15 and 20 or 30 and35
wherever possible. If the number of blows was between 20 and 30 in all2
-The results of this study have led us to adopt the one-point method as a standard test in our laboratory, subject to the following ｲ･ｳｴｲｩ｣ｴｩｯｮｳｾＭ
(i) It should not be used on soils which contain an appreciable amount of organic mater, or
(ii) where special accuracy is required of the test, three or more points should be used.
Appendix A to this note gives the procedure which is being used
currently in the Soil Mechanics ｬ｡｢ｯｲ｡ｴｯｲｹｾ Division of Building Research .. N. R. C. The coefficients used for determining the Uquid limits are
listed. These coefficients are for the equation: L.L.
=
Wn. Ntan B3
where tan B
=
0.100Wn
=
Water content at N blows N=
No. of blows.This note is nresented with the hope that it will stimulate further comparisons of the conventional and the one-point liquid limit method as suggested by Olmstead. Considerable savings in the cost per
determination can be effected, without seriously impairing the accuracy of the test. By repeating the mixing, groovin and testing as outlined in Step
8
of the procedure, gross errors can be prevented.Acknowledgements
The writer wishes to acknowledge the assistance of J.C. Plunkett and W.D. Murray in compiling the data given.
References
1) Correlation of Soil Properties With Geological Information, Report No. III "Simplification of the Liquid Limit Test Procedure"
Technical Memorandum No.
3-286,
Waterways Experiment Station, Vicksburg Miss., June1949.
2) Olmstead, F.
no
D & Johnston, C. M. "Rapid Methods for DeterminingLiquid Limits of Soils", Bulletin
95, pa27-37,
Highway Researchｂｯｾｲ､Ｌ Washington,
1955.
3)
Proceedings of the Eighth Canadian Soil Mechanics Conference, Technical Memorandum No.36,
Associate Committee on Soil and Snow Mechanics, National Research Council, Canada,1955.
APPENDIX A
Suggested Procedure for Liquid Limit ｾｲｭｩｮ｡ｴｩｯｮ
The liquid limit denotes that moisture content at which a sample of soil just passes from a liquid to a plastic state. It is arbitrarily chosen as the moisture content at Which two sections of a pat of soil begin to flow together when subjected in a cup to the impact of 25 sharp blows from below. To eliminate the personal element, which usually has an important influence in this test, a standardized mechanical device is used ..
Equipment
I mortar and rubber-covered pestle 1 U.S.S. No. 40 sieve
1 evaporating ､ｩｳｨｾ medium 1 spatula
1 wash bottle and distilled water 1 liquid limit device
3
or 4 Casagrande grooving tools 1 or 2 metal weighing tins1 Chainomatic balance
1 cons ant t t empera ure oven,t 1050 - 1100C ..
1 desiccator
Procedure
The test is often performed on a soil sample in its natural state. If the sample has begun to dry out, however, i t should be thoroughly air-dried and tested from the air-dried state. A sample which has preViously been oven-dried, or a sample whose "drying history" is unknown, should never be used. Note the original conditions of the sample on the data sheet for "Atterberg Limitstt which is used.
I. Choose a representative sample of 150 to 200 gm. of soil. If this sample is in the natural moist state, remove all particles larger than 1/16th inch with the fingers. If the sample has been air-dried, grind i t in a mortar, using a rubber-covered pestle, and pass it through a No. 40 sieve to remove the coarse particles. 2. Mix the sample in a medium evaporating dish to the consistency of
a very thick paste, using distilled water ..
3.
Cover the dish and allow the soil to soak, preferably overnight. Record the time of soaking on the data sheet.---...
A - 2
4&
Using the handle of the grooving tool as a gauge, check the liquid limit device to ensure that the height of fall of the cup isexactly 1 cm og and adjust if necessary. This should be the vertical distance from the centre of the worn spot on the cup to the solid basey when the crank is just about to drop the cup.
Set the device in a predetermined spot on a table of sturdy
construction, where it will remain throughout the test. (See page 152 ｾ Soil Testing for Engineers by Lambe for illustration of
adjustment of device).
5.
Place some of the soil sample in the cup of the liquid limit device to a depth of3/8
ｩｮ｣ｨｾ being careful not to entrap any air bubbles, and smooth the surface with a spatula so that it is horizontal when the cup is at rest in the device.6.
Take the cup in the palm of one hand o Holding the grooving tool perpendicular to the surface of the cup, and starting at the back, cut a groove in one continuous motion along the diameter through the centre line of the cam follower. In silty and sandy soils it may sometimes be necessary to cut the groove with a spatula orspecial tool, using the grooving tool to check dimensions.
7.
Place the cup gently in the liquid limit device. Turn the handle at approximately 2 turns per second until the bottom of the groove is closed for a distance of 1/2 inch, and record the number ofblows. To ensure that the handle is rotated smoothly, the operator should stand facing the handle of the device. The number of blows must lie between 15 and
34
before proceeding with the testo More blows than34
require the addition of distilled water and remixing while less than 15 blows requirffi air drying.8.
Repeat the operation of mixing in the cup, grooving and testing until three successive determinations show logical agreement with a diff-erence of not more than one or two blows. Record the number of blows for these last three determinations.9.
Immediately transfer a minimum of 10 gms. of the soil from the Vicinity of the closed groove to a weighing tin and cover the tin. 10. Weigh the tin containing the sample to the nearest 0.01gm.
andrecord o
II.
Dry
the open tin in the oven overnight.12. After drying, replace cover and place in the desiccator to cool and then weigh to 0.01 gm.
13. Compute the water content based on the dry weight of the soil. The liquid limit is then computed by multiplying the water content at N blows by ｾｨ･ coefficient corresponding to N blows.
