Resumen de Analysis of underground excavations in argillaceous hard soils - weak rocks
Stiff clayey materials, lying in the transition between hard soils and weak rocks, are being currently considered in several countries as possible host medium for deep geological disposal of high active and long-lived nuclear waste. This possibility has led to the construction of underground research laboratories (URL), excavated in these indurated clayey materials, to study their behaviour under real working conditions. Among the very different topics addressed in the URLs, the hydromechanical behaviour of the host rock is the one that most concerns the present research. In situ observations have revealed that excavation operations induce damage around the galleries, in the form of fracture networks, contained within a zone called excavation damaged zone (EDZ). The EDZ has been identified as one of the main aspects affecting the behaviour of the excavations. In this context, the main objective of the present study is the numerical simulation of the hydromechanical behaviour of experimental excavations performed at the Meuse/Haute-Marne URL (France). For this purpose, a constitutive model has been developed to characterise the host formation. The modelling of these stiff argillaceous materials is a quite challenging task. They exhibit soil-like features like considerable plastic strains, rate-dependency, and creep, although they also show characteristics more typical of a rock such as significant softening and localised deformations. In addition, due to their sedimentary origin, they often exhibit anisotropy in properties like stiffness, strength, and permeability. Special attention has been paid to the reproduction of the EDZ and, therefore, to the objective simulation of localised deformations; a nonlocal approach has been employed for the regularisation of the continuum, avoiding the dependence on the employed mesh. The obtained results provide relevant insights into the hydromechanical behaviour of these stiff clayey materials, and they indicate the main aspects affecting the response of the underground excavations. In particular, the relevance of the EDZ has been demonstrated.
