Geomechanical behaviour of Boom clay under ambient and elevated temperature conditions

This research item is focused upon in-situ investigations related to the (thermo-) mechanical behaviour of clay. Three main items are covered in this research area : - stress measurements around the Underground Research Facility (URF) using hydraulic stress monitoring stations; - detection of micro-fractures in the clay host, mainly using geophysical seismic techniques; - long term mechanical behaviour of clay; this last item was investigated at Mol by ANDRA/G3S; dilatometer devices were installed in access holes drilled in clay from the URF. This report essentially describes the investigations carried out and results recorded by CEN/SCK for the two first items. The stress monitoring stations appear to be more reliable in getting relative pressure variations with time rather than absolute values of stress, even after studying and improving the characteristics of the surrounding grout. The seismic techniques used appear to be sensitive and accurate enough for detecting induced fracturation in the clay host, even for the low temperature gradients here assumed; this is also in agreement with laboratory measurements on clay samples intended to quantify the influence of both temperature and consolidation on the velocity.