An evaluation of the osmotic method of controlling suction

TL;DR

This paper reviews the osmotic technique for controlling suction in unsaturated soil testing, discussing its advantages, drawbacks, and recent developments, and compares it with the axis-translation method.

Contribution

It provides a comprehensive evaluation of the osmotic technique, including recent advancements and novel applications in geotechnical testing.

Findings

Osmotic method offers realistic suction conditions and higher suctions.

Advantages include ease of attaining high suctions and relevance to natural conditions.

Drawbacks involve membrane resistance and calibration effects.

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 axis-translation 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.