An evaluation of the osmotic method of controlling suction∗

Abstract

Tel. 33 1 64 15 35 42, fax 33 1 64 15 35 42 2 Abstract : Experimental techniques of testing the mechanical properties of unsaturated soils are complex and difficult to conduct. As a consequence, complete sets of parameters that characterise the behaviour of unsaturated soils remain scarce and necessary. In this context, it has been found useful to gather the information obtained after some years of practice of the osmotic technique of controlling suction. As compared to the more documented axistranslation technique, the osmotic technique has its own advantages and drawbacks that are discussed in this paper, together with some potential future developments.The osmotic method has been developed by soil scientists in the 1960s and adapted to geotechnical testing in the early 1970s. This paper presents the osmotic technique and comments on its advantages (including suction condition close to reality and higher suctions easily attained) and drawbacks (including some concern with the membrane resistance and some membrane effects in the suction/concentration calibration). Various applications to geotechnical testing are presented such as the determination of the water retention curve, oedometer and triaxial testing procedures and the determination of the permeability of unsaturated soils. Recent developments, that include the extension of the method up to high suctions (10 MPa) are also described, together with some recent and novel applications such as data from high controlled suction oedometer compression test and the determination of the oil/water retention properties of oil reservoir chalks.

Geoenvironmental Testing

“…Standard experimental techniques used in unsaturated soils to control suction (axis translation, osmotic and vapour equilibrium techniques) have been adapted and used for hydro-mechanical testing at elevated temperatures. Axis translation and osmotic techniques are limited to low suctions (below 1.5 MPa when using axis translation with standard high air-entry value (HAEV) ceramic discs, and below 9 MPa (Delage et al 1998a;Delage and Cui 2008) when using the osmotic technique), whereas vapour equilibrium covers with reasonable precision the upper suction range from 3 to 1000 MPa. Axis translation technique has demonstrated its applicability to study the combined effects of partial saturation and temperature on hydro-mechanical soil behaviour.…”

Investigation of the hydro-mechanical behaviour of compacted expansive clay

“…In order to investigate the hydro-mechanical behaviour of compacted expansive clay in laboratory, suction-controlled oedometer tests are usually performed. In these tests, soil suction was controlled using various techniques, such as axis translation technique [7], osmotic technique [8][9][10], and vapor equilibrium technique [11], depending on the suction range involved by the soil studied. The experimental results in terms of volume changes upon coupled hydro-mechanical loading are usually interpreted by using the BExM model [11][12][13].…”

On the intrusion of polyethylene glycol during osmotic tests

“…Several researchers have used the osmotic technique to study the water retention behaviour of soils (Fleureau et al 1993;Marcial et al, 2002;Williams & Shaykewich, 1969;Zur, 1966). Similarly, the technique has been used to study the volume change behaviour of soils as affected by changes in the soil suction (Cui & Delage, 1996;Cuisinier & Masrouri, 2005;Delage & Cui, 2008a;Delage et al, 1998;Dineen & Burland, 1995;Kassiff & Ben Shalom, 1971;Monroy et al, 2007).…”