ABSTRACT
This paper presents the results of an experimental investigation aimed at evaluating the effects of hydraulic cycling on the small-strain stiffness of a rigid Jurassic clay (Opalinus clay, Switzerland). This clay was previously subjected to thermal loads during an in situ heating experiment (HE-D, Gens et al. 2007). After this in situ test, intact samples were retrieved and analysed at laboratory scale. In a first stage, the influence of thermal loads was studied to evaluate the initial state of the samples prior to hydraulic cycling. In a second stage, samples at different distances to the heater were subjected to wetting and drying paths using vapour equilibrium technique. The hydraulic effects were tracked at macroscopic scale using basic characterisation (water content and porosity) and non-destructive techniques (ultrasonic pulses and bender elements). Test results showed a noticeable change of stiffness with total suction. An expression to account for seismic velocity changes with total suction is proposed.
