Numerical modelling of self-sealing in fractured clayey materials

The network of fractures generated during the excavation of underground research facilities can induce stress redistribution and alteration of flow and transport properties, becoming preferential paths for releasing radionuclides into the host rock.

However, in the long term, the fractures can be sealed through the resaturation of water coming from the rock as a function of its self-sealing potential. Despite the large number of experimental studies that have proven the self-sealing capacity of clay rocks, very few attempts have been made to describe and predict the phenomenon numerically. This may be due to the difficulty of measuring the initial hydromechanical conditions. Additionally, samples artificially fractured in the laboratory can be disturbed by the preparation process itself, which can alter the hydromechanical state. This paper addresses that issue by bridging the gap between experiments and numerical modelling. Representative experimental tests performed on Callovo-Oxfordian Claystone (COx) are used to offer a hydromechanical fracture law that takes into account the self-sealing capacity of the material. Implementing such a model in a finite element code allows its validation through comparison with laboratory tests. Furthermore, the role of the initial fracture size and the evolution of water permeability during the wetting/drying process are investigated. Due to its transmissivity, injected water can penetrate the rock, initially reaching the damaged zone around the fracture before spreading through the entire sample. This progression is accounted for in the constitutive equation and represented numerically. Nevertheless, a larger initial crack leads to reduced recovery rates. These results match the experiments, offering a valuable perspective on the modelling of self-sealing in in-situ conditions.