Determination of the shear strength parameters of an unsaturated soil using the direct shear test

Determination of the shear strength parameters of an unsaturated soil using the direct shear test

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Determination of the shear strength parameters of an unsaturated soil using the direct shear test J. K. M. GAN Minconsult Sdn. Bhcl., 14 Jalan 20/16A, Paratnount Gc~rdetz, 46300 Peralitlg Jnyn, Selrngor, Malaysin AND D. G. FREDLUND H. RAHARDJO Depclrtmetzt of Civil Etzgitzeeritzg, Utziversity of Sc~skelrcke~~an, Saskatoon, Sr~sk., Carlacla S7N OW0 Received May 20, 1987 Accepted March 17, 1988 Multistage direct shear tests have been performed on saturated and unsaturated specimens of a compacted glacial till. A con- ventional direct shear apparatus was modified in order to use the axis-translation technique for direct shear tests on unsaturated soils. The soil can be subjected to a wide range of matric suctions. The testing procedure and some typical results are pre- sented. Nonlinearity in the failure envelope with respect to matric suction was observed. Suggestions are made as to how best to handle the nonlinearity from a practical engineering standpoint. Key words: shear strength, unsaturated soils, negative pore-water pressures, soil suction, direct shear. Des essais en cisaillement direct B Ctapes multiples ont CtC rCalisCs sur des spkcimens saturCs et non saturCs de till glaciaire compactC. Un appareil conventionnel de cisaillement direct a CtC modif6 de fa~on B utiliser la technique de translation d'axe pour des essais de cisaillement direct sur des sols non saturCs. Le sol peut &tre assujetti B un large domaine de succion de matrice. La procCdure de I'essai et quelques rksultats typiques sont prCsentCs. Une non-IinCaritC de l'enveloppe de rupture en fonction de la succion de matrice a CtC observCe. Des suggestions sont faites quant B la meilleure fa~on de tenir compte de cette non-IinCaritC du point de vue de I'ingCnieur. Mots cle's : rksistance au cisaillement, sols non saturCs, pressions interstitielles nkgatives, succion du sol, cisaillement direct. [Traduit par la revue] Can. Geotech. J. 25, 500-510 (1988) Introduction Most man-made earth structures involve the use of com- pacted soils. The compaction process produces a soil with a degree of saturation usually in the range of 75 -90%. Earthfill dams, embankments, and highways are typical examples of earth structures made of compacted, unsaturated soils. The theory and measurement of shear strength of unsaturated soils have gained increasing attention during the past three decades. A brief review on the development of our understanding of the shear strength behavior of unsaturated soils is presented in this paper. This paper presents the results of a series of direct shear tests on an unsaturated soil. Direct shear testing of unsaturated soils is desirable since less time is required to fail the soil specimen than when using the triaxial test. The time to failure in the direct shear test is greatly reduced because the specimen is relatively thin. The lengthy testing period for unsaturated soils is due to the low coefficient of permeability of the soil and the high air entry disc in contact with the specimen.
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This note was uploaded on 02/20/2012 for the course ENGINEERIN 14:180:372 taught by Professor Gucunski during the Spring '11 term at Rutgers.

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Determination of the shear strength parameters of an unsaturated soil using the direct shear test

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