NorEs 29'7

THE CASAGRANDE METHOD VERSUS THE DROP-CONEPENETROMETER METHOD FOR THE DETERMINATION OF LIQUID

LIMIT

A comparison of the drop-cone penetrometer and Casagrande methods for deter-mining the liquid limit of soils showed that the former method is simpler, fasterand provides more precise results.

Key words: Casagrande, drop-cone penetrometer, liquid limit, soil survey

[comparaison entre les m6thodes de casagrande et du p6n6trombtre d c6ne dansla d€termination de la limite de liquiditd.lTitre abr6g6: D6termination de la limite de liquidit6.La comparaison entre les m6thodes du p6n€tromdtre i c6ne et de casagrande pourd6terminer la limite de liquidit6 de certains sols a r6v6l6 que la premidre m6thodeest plus simple, plus rapide et plus pr6cise.

Mots cl6s: Casagrande, p6n6tromEtre d c6ne, limite de liquidit6, prospectionp6dologique

The liquid limit of soil samples is meas-ured periodically in soil survey laborato-ries in Canada using the Casagrandemethod, ASTM 423-66 (McKeague t9't8).The Casagrande method has many short-comings such as difficulty of cutting anideal groove, the necessity to estimate theamount of groove closure, slow speed ofoperation (Sowers et al. 1960; Hanks1981). A newer method using a drop-conepenetrometer is the standard method in soilmechanics laboratories in Great Britain(BS 1377, 1975). The drop-cone penetro-meter yields liquid limit results comparableto those obtained by the Casagrandemethod but with less variability due to op-erator technique according to Sherwoodand Ryley (1968). The drop-cone penetro-meter has not been tested in Canadian soilsurvey laboratories though the require-ments for measurement of "engineering"properties of soils is increasing.

The purpose of this work was to comparethe suitability of the drop-cone penetro-meter and the Casagrande methods in a soilsurvey laboratory where liquid limit deter-mination would be required periodically.Simplicity of operation, speed and preci-sion of analysis were considered to be im-Can. J. Soil Sci. 642 297-3O0 (May 1984)

portant attributes of a suitable method.The test samples were four C horizon

materials with texture ranging from loamto heavy clay; the bulk samples were air-dried and sieved to less than 425 pm. Thesamples were prepared for testing follow-ing the procedure in ASTM 423-66 (1979).Analysis time (r) was based on predeter-mined starting and finishing points com-mon to each method. Standard methods BS1377; 1915 (drop-cone penetrometer) andASTM 423-66 (19'19) (Casagrande) weretested as follows: (i) an operator (A) withsimilar experience in using the two meth-ods determined the liquid limit of each soilmaterial l0 times by each method; (ii) twooperators (C and D) experienced in usingthe Casagrande method analyzed each ofthe four materials in duplicate by thatmethod; (iii) an inexperienced operator (B)analyzed each of the four materials in du-plicate using the drop-cone penetrometermethod.

Operator A obtained more precise resultsin less time with the drop-cone penetro-meter than with the Casagrande method(Table 1). Mean values by the two methodswere similar for all samples but those bythe Casagrande method were slightlyhieher.

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300 CANADIAN JOURNAL OF SOIL SCIENCE

An inexperienced operator (B) using thedrop-cone penetrometer reported liquidlimit values similar to those of operator Abut required more than double the time tocomplete the measurement (Table 2). Ex-perienced operator C, using the Casa-grande method, obtained liquid limit val-ues similar to those of operator A, but theliquid limit values of operator D (also ex-perienced) were higher than those of op-erator C (Table 2).

Overall, the data show that similar liquidlimit values are obtained by the two meth-ods, a narrower range in the drop-cone pe-netrometer data, as compared to the Cas-agrande data. indicates more precisionwith this method. In addition, as shown inTable 1, an experienced operator can de-termine liquid limit by the drop-cone pe-netrometer method in approximately 6OVo

of the time required using the Casagrandemethod. The drop-cone penetrometermethod is recommended for the determi-nation of liquid limit in soil survey labo-ratories in Canada.

Technical assistance provided by B. K. Hohner,A. M. Pushman and E. Vendette of the LandResource Research Institute, AgricultureCanada is gratefully acknowledged.

ASTM D 423-66. 1979. Standard test methodfor liouid limit of soil. Annual Book of ASTMStandirds, Philadelphia, Pa.BS 1377. 1975. Methods of test for soils forcivil engineering purposes (Test 2a and 2c).British Standards Institute, London, U.K.HANKS, A. J. 1981. Measurement of the liquidlimit of soils using the cone penetration method.Ont. Ministry of Transportation and Commu-nication, Engineering Materials Office, Soilsand Aggregates Section, Toronto, Ont.McKEAGUE. A. J. (ed.) 1978. Manual on soilsampling and methods of analysis. CanadianSociety of Soil Science, Ottawa, Ont. 212 pp.SHERWOOD. P. T. and RYLEY, M. D. 1968.

An examination of cone-penetrometer methodfor determining the liquid limit of soils. Road

Research Laboratory Report LR233.SOWERS, G. G., VESIX, A. and GRAN-DOLFI, M. 1960. Penetration test for liquidlimit, ASTM Special Publication No. 254, Phil-adelphia, Pa. pp. 216-226.

K. C. WIRESLand Resource Research Institute, Re-

search Branch, Agriculture Canada,Ottawa, Ontario KIA 0C6. Contributionno. 82-67 , received 26 July 1983 , accepted20 Jan. 1984.

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