Effects of heating and hydraulic cycling on the stiffness response of a rigid ansiotropic clay: preliminary results

Abstract

The poster presents the results of an experimental investigation aimed at evaluating the effects of heating and hydraulic cycling on the small-strain stiffness of a rigid Jurassic clay (Opalinus clay, Jura Mountains, Mont Terri Underground Laboratory, Switzerland). This clay was subjected to thermal loads during an in situ heating experiment (HE-D). After the test, intact samples were retrieved and analysed at laboratory scale. The influence of thermal loads was studied using basic characterisation, microstructural techniques (MIP) and non-destructive techniques (ultrasonic pulses). The retrieved samples were then subjected to wetting and drying paths. The hydraulic effects were tracked using basic characterisation (water content and porosity) and non-destructive techniques (ultrasonic pulses and bender elements). Test results showed a higher sensitivity of stiffness on suction increase for the material less affected by the thermal load (far from heater). Tests are currently being carried out on a new and fully instrumented high-pressure triaxial cell to monitor degradation effects induced by hydraulic cycling under a controlled stress field. Degradation is monitored by horizontal and vertical bender elements to track different directions.