On the THM behaviour of a sheared Boom clay sample: Application to the behaviour and sealing properties of the EDZ

In this study the effect of the temperature increase on the hydro-mechanical properties of sheared Boom clay samples is investigated. Two samples of Boom clay are resaturated in a new hollow cylinder triaxial cell with a short drainage path and then sheared by performing an axisymmetric triaxial loading. The effect of the undrained heating under deviatoric stress is studied on the first sample. It is shown that undrained temperature increase leads to an increase of pore water pressure and consequently to a decrease of the effective mean stress which brings the sample to failure. For an initially sheared sample, the failure occurs along the existing shear band which behaves as a weakness plane in the sample. The responses of the local strain measurement transducers clearly show the sliding of rigid blocks when failure occurs in the sample.The effect of the presence of a shear band on the permeability of the other Boom clay sample is investigated at ambient temperature and at 80 °C. It is shown that the presence of a shear band does not affect significantly the permeability. These results confirm the good self sealing properties of Boom clay at ambient and at high temperature.

► A new hollow cylinder cell with a short drainage path is used to study the THM behaviour of Boom clay.
► Reactivation of a failure plane through the thermal pressurization of the pore fluid during undrained heating is evidenced.
► The good self sealing properties of Boom clay are confirmed through permeability measurements at ambient and high temperature.