Fatemeh Salehnia

Numerical modelling of the excavated damaged zone in Boom Clay

There is an international consensus on the advisability of storing high-level nuclear waste in the deep geological repository with low permeability. Boom Clay which is characterized by low hydraulic conductivity and the self-sealing capacity is known as one of the potential host rock for this geological disposal process. The excavation process in deep geological host rocks is expected to create a perturbed zone around the underground structures in rock masses in which the significant irreversible deformations and significant properties changes can be occurred. Modelling of the fracturing system and extension of the so-called Excavation Damaged Zone EDZ as an essential issue is focused in this study using the strain localization approach as a classical mode of failure of geo-materials. Numerical modelling of strain localization needs a specific approach to overcome the practical problem of mesh size dependency within the framework of classical finite elements. The second gradient method is used in this study in order to overcome this problem. Coupled numerical modelling of a gallery excavation in in Boom Clay host rock is performed. The simulation provides information about the strain localization in shear bands mode accomplished by the evolution of EDZ during the gallery excavation.

On the Variable Dilatancy Angle in Rocks Around Underground Galleries

Correct estimation of the dilatant behavior of a rock has an essential role in a realistic numerical simulation of the fracturing threshold during the rock deformation process and its post-failure response, based on experimental and field observations. This importance has been poorly treated in most of the numerical analyses dealing with the rock engineering common problems such as deep excavations. The dilatancy angle as a commonly used parameter for describing the dilatation response of a rock is mostly simplified to be a constant value. Contrarily, a literature review declares the inadequacy of this approach in those rock mechanics applications. In the present paper, a new formula for considering the variable dilatancy angle is presented which relates this parameter to the plastic shear strain in the course of a loading procedure. It is aimed at characterizing an evolution of the dilatant or contracting volumetric response of a rock as well as giving the possibility to simulate a dilatant/contracting transitional behavior. The model is applied to simulate the development of strain localization, in shear band mode, within the inevitable excavation damaged zone created around an underground opening in rock. It is illustrated that using the model of variable dilatancy angle in a deep excavation modeling could help to better reproduce the fractures development around the opening in the course of tunneling.