A series of experiments were performed to characterize the permeability,
the specific storage, the capillary pressure, the streaming potential
coupling coefficient, and the electrical conductivity of a very low
permeability Callovo-Oxfordian clay rock at different water saturations.
The Callovo-Oxfordian formation is presently investigated as a potential
host to store nuclear wastes because of its very low permeability
(typically 10 nd at saturation) and high specific surface area. We
first present the constitutive transport equations including an electrokinetic
cross-coupling term in the generalized Darcy and Ohm constitutive
equations. Then we present new experimental results using measurements
of transient weight losses of samples submitted to a change in the
relative humidity imposed by an automated humidity system in a hermetic
chamber. These experiments are interpreted with a 1-D analytical
model of the coupled hydromechanical and transport equations. The
hydromechanical transport properties (relative permeability and specific
storage) of this clay rock are investigated in the relative saturation
range from 0.23 to 0.70. We demonstrate that below 30% in relative
humidity, the flux of the vapor phase with respect to the flux of
the liquid water phase cannot be neglected. The relative apparent
permeability can be described by a simple power law relationship
with the saturation. In addition, we measure the electrical conductivity
and the streaming potential coupling coefficient at various saturations.
The electrical conductivity is described by a model accounting for
electrical double-layer contributions to surface conductivity. The
measurement of the streaming potential coupling coefficient agrees
with a power law model for the coupling coefficient versus the relative
water saturation. A relationship between the exponent used to characterize
the relative permeability and the second Archie's exponent used to
describe the dependence of the electrical conductivity of the material
with respect to the saturation is discussed.