Hydromechanical modelling of an excavation in an underground research laboratory with an elastoviscoplastic behaviour law and regularization by second gradient of dilation

In the context of nuclear waste disposals, this paper deals with hydromechanical modelling in saturated conditions in deep geological formation, using a specific elastoviscoplastic model hereafter called the L&K model. While classical Biot's framework is followed for the hydromechanical coupling, the mechanical L&K model offers a coupling between instantaneous and delayed behaviour and a variation of dilation often related to softening. These volumetric strains are especially highlighted in coupled hydromechanical conditions. In order to avoid mesh dependency and numerical localized solutions, this type of modelling needs the use of a regularization method which is here referred to as the second gradient dilation model. After describing the numeric tools, we use them for simulating a gallery of the underground research laboratory of Bure. The approach is validated by the good general agreement found between numeric results and in situ measures for both hydraulic pressure and displacement.

► We model delayed behaviour of an excavation in the context of geological nuclear waste storage.
► Modelling is performed with hydromechanical coupling and regularization.
► The constitutive law for the rock mass is an elastoviscoplastic one called L&K.
► Comparisons of water pressures and displacements with in situ measures validate simulations.