Desiccation and Rehumidification Effects On The Thermohydromechanical Behaviour of the Callovo-Oxfordian Argillaceous Rock

Abstract This paper presents experimental results concerning the impact of changes in relative humidity or water content on the mechanical properties of an argillaceous rock. The rock under investigation, known as Callovo-Oxfordian argillites, is situated at a depth of 500 m in Eastern France. An underground research laboratory is being built since 2000 by Andra for a feasibility study on deep geological disposal of high-level long-lived radioactive waste. Two contradictory desiccation effects are observed: i) hardening of the rock, and ii) damage due to micro-cracking associated with desiccation. The amplitude of these two phenomena in the argillaceous rock depends on the changes in relative humidity. For example, a decrease from 100% to 60% in relative humidity may multiply the Young's modulus of the rock by five. Meanwhile, the uniaxial compression strength of the rock becomes three to four times higher due to the humidity decrease, strain (shrinking) induced by the change of relative humidity may reach 0.5%