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Abstract. The French national radioactive waste management agency (Andra) research program is dedicated to preparing the construction and operation of a deep geological disposal facility for high-level and intermediate-level long-lived radioactive waste (HL, IL-LLW) in the Callovo-Oxfordian claystone (COx). The characterization of the COx thermo-hydro-mechanical (THM) behavior, at different scales of interest, must gradually give relevant data for design and safety calculations. The effects of saturation and desaturation of COx claystone are studied in laboratory conditions (sample scale) and in situ (drift scale), in order to improve knowledge on ventilation effect at gallery wall as galleries will remains open during operational phase (more than 100 years for some specific galleries) in the repository. The Saturation Damaged Zone (SDZ) experiment is outlined and its results are discussed. This experimentation aims to change the relative humidity in an isolated portion of a gallery in order to follow the HM behavior of the surrounding rock mass. Drying and wetting cycles could induce in certain cases cracks and swelling and modify the hydromechanical behavior of the claystone around the gallery (Young modulus, strength, creep…). The long term behavior of the COx claystone at the vicinity of gallery is then studied by performing climatic, hydraulic, geological and geomechanical measurements. Results of the in situ experiment are discussed with respect to the identified process on samples. The discussion given on this paper intends to highlights the inputs from 7 years of an in situ experiment to better understand the unsaturated behavior of the COx claystone.

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We focus herein on the mechanical behavior of highly crushable grains. The object of our interest, named shell, is a hollow cylinder grain with ring cross-section, made of baked clay. The objective is to model the fragmentation of such shells, by means of discrete element (DE) approach. To this end, fracture modes I (opening fracture) and II (in-plane shear fracture) have to be investigated experimentally. This paper is essentially dedicated to mode I fracture. Therefore, a campaign of Brazilian-like compression tests, that result in crack opening, has been performed. The distribution of the occurrence of tensile strength is shown to obey a Weibull distribution for the studied shells, and Weibull's modulus was quantified. Finally, an estimate of the numerical/physical parameters required in a DE model (local strength), is proposed on the basis of the energy required to fracture through a given surface in mode I or II.

This paper addresses the microstructure change induced by swelling for natural stiff Teguline clays. The predominant clay mineral measured by X-ray diffractometry was identified to be illite and no swelling clay minerals were found. Significant swelling occurs upon wetting, illustrating the process of suction release from a nearly fully saturated condition. Mercury intrusion porosimetry (MIP) and scanning electron microscopy were used to identify the change in microstructure with swelling during wetting. It is found that the soil swelling mainly leads to an increase of macropores (0.15–350 μm), and a slight decrease of micropores (0.006–0.15 μm) and inaccessible pores (<0.006 μm and >350 μm). Furthermore, swelling was found to occur in the direction perpendicular to the bedding plane, indicating an anisotropic swelling behaviour. The creation and development of cracks during wetting were also investigated. It appears that most cracks caused by swelling have the size of macropores (0.15–350 μm) identified by the MIP test. These findings call enough attention to the significant change in microstructure by wetting-induced swelling that can strongly influence the thermohydromechanical properties of stiff clays.