Recent developments in the osmotic technique of controlling suction

The osmotic technique of controlling suction provides an alternative to the more commonly used << axis -translation >> technique. This technique is based on the use of an aqueous solution of big sized polyethylene glycol molecules (PEG) and of a semipermeable membrane. In the paper, the principles of the technique are described, and the various applications to geotechnical testing are commented : retention curves, oedometer and triaxial suction controlled apparatuses. The main advantage of the technique is that no artificial air pressure is applied to obtain a positive value of the suction (S = u(a) - u(w)), as in the reality. It is now possible to reach suction as high as 12 MPa without any safety problem related to the confinement of high air pressures. The drawbacks of the technique are mainly related to the weakness of the membrane, and the paper explaines how most of them can be corrected.