Abstract : The present thesis aims to study the visco-hydro-mechanical behaviour of Estreux chalk through scale effects (in situ, the sample and the microstructure) for the research of “Aging phenomena of rock masses”. Firstly, one square pillar in Estreux abandoned underground mine has been continuously monitored since February 2004. These measurements allow reproducing the seasonal environmental changes (i.e. hygrometry ranges between 80 and 100%) for laboratory testing. Secondly, an experimental work on the water retention properties was performed. This study showed that changes of the relative humidity in the Estreux mine between 80% and 100% can generate important changes of the state of saturation of the Estreux chalk, at least at the surface of the pillar in contact with the relative humidity of the atmosphere. Therefore, in a third step the mechanical response of the partially saturated chalk has been characterized by running a series of high pressure controlled suction oedometer and triaxial tests. The viscous behaviour of the chalk has also been studied mainly by a campaign of triaxial test at different rates. The results showed the suction and rate effects on the mechanical behaviour of chalk: as the suction, the rate effect causes an expansion of the yield stress of chalk with increasing rate. Fourthly, these phenomena have been compared to the microscopic scale. After a study on the definition of a protocol on observations by an environmental scanning electron microscope (ESEM), a controlled suction system of a loading module compression / tensile Microtest (Deben ®) installed in the observation chamber of ESEM was developed. With this system, the visco-hydro-mechanical behaviour of chalk on a microscopic scale has been investigated. Finally, this behaviour was modelled by developing on triaxial space of RASTRA model (Rate if strain model) (De Gennaro & Pereira, 2008). This model was used to simulate both the suction and time effects.