Design of triaxial test with controlled suction: measure of strain

Experimental study of mechanical behaviour of clayey materials under hygrom etric condition is usually performed either on unloaded samples or by means of classical oedometer tests used in soil mechanics. Such methods are not well adapted to hard deep clayey rocks with little deformability, porosity and permeability. Moreover, stress and strain tensors having a significant effect on hygro-mechanical behaviour and properties cannot be measured and investigated appropriately by classical tests. This is why a specific triax ial test was designed in which the sample is surrounded by a fiber glass ti ssue allowing air circulation and then by silicon on which confining pressu re is applied. Thus, equilibrium between air and sample was reduced. Stress and strain tensors were also measured in time on the sample subjected to a mechanical loading and to a controlled suction. After presentation of the test, preliminary results are given. (C) 2000 Academie des sciences / Editi ons scientifiques et medicales Elsevier SAS.