technote bouyancy - . -. TECHNICAL NOTE Jean-Pierre Bardet...

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. -. TECHNICAL NOTE Jean-Pierre Bardet’ und Julie Young’ Grain-Size Analysis by Buoyancy Method REFERENCE: Bardet, J.-E? and Young, J., “Grain-Size Analysis by Buoyancy Method,” Georechnicaf Tesring Journal, GTJODJ, Vol. 20, No. 4, December 1997, pp. 481-485. ABSTRACT: A new routine experiment referred to as buoyancy anal- ysis is proposed to determine the grain-size distribution of tine-grained soils. The buoyancy analysis is based on the sedimentation principles of the hydrometer and pipette analyses. It determines the percent by weight finer than a given grain size by measuring the buoyant weight of a 2.5cm-diameter sphere immersed in the soil suspension. The buoyancy analysis is slightly more accurate than the hydrometer analy- sis, has a shorter duration, and its readings can be fed directly into a computer. It yields results identical to those of the hydrometer analysis when the sphere is immersed within the depth range of the hydrome- ter bulb. KEYWORDS: sedimentation, particle size, buoyancy, grain-size dis- tribution, soil testing In geotechnical engineering, the grain-size distribution of fine- grained soils is usually determined by performing routine tests such as the hydrometer (Weatherly 1929; ASTM 1995) and pipette (BS 1975; Head 1984) analyses. Both analyses assume that the sedimentation process of small soil particles follows Stokes’ law (Stokes 1891), and that the soil particles fall under their own weight as non-interacting spheres (Bardet 1997). The hydrometer analysis typically lasts at least 24 h and requires the calibration of the hydrometer and corrections for temperature variation, menis- cus, and dispersing agent. The pipette analysis, which is based on the same physical principle as the hydrometer analysis, is about twice as fast because the sedimentation distance can be reduced, but requires additional experimental care, especially when drawing the soil samples and emptying the pipette contents. Some refine- ments of the pipette analysis were proposed by Moshrefi (1993) to minimize the disturbance of the sedimentation process. The practical shortcomings of both hydrometer and pipette analyses are numerous experimental steps and manual readings, which are difftcult to feed automatically into computers. Such shortcomings prompted Zhang and Tumay (1995) to computerize granulometric analysis by measuring suspension pressure. There are other methods besides hydrometer and pipette analyses for obtaining the grain-size distribution of fine-grained soils. These include the sedimentation balance method, photo-sedimentation, X-ray sedimentation, and centrifugal sedimentation techniques ‘Professor and research assistant, respectively, Civil Engineering Department, University of Southern California, Los Angeles, CA 90089-253 1.
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This note was uploaded on 04/26/2010 for the course BLAW law taught by Professor Blllas during the Spring '10 term at University of Louisiana at Lafayette.

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technote bouyancy - . -. TECHNICAL NOTE Jean-Pierre Bardet...

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