Three-dimensional and time stepping modelling of the whole Meuse Haute Marne URL
Résumé
The Meuse Haute Marne underground research laboratory of Meuse (ANDRA) is constituted by several shafts and drifts. The whole of the laboratory is mainly located in a volume of several millions cubic meters in the Callovo-Oxfordian geological layer. The shafts and the various drifts form a complex structural design. In order to see possible interference between drifts and shafts and to assess the in situ stresses in specific areas of the laboratory. a numerical study was performed to model the mechanical behaviour of the whole drifts by using a chronological sequence of the excavations, close to what was actually realised. Numerical modelling, with considering the geometric scale of the problem, was carried out by finite elements with relatively simple constitutive models describing the argillites. It is on the one hand a linear isotropic elastic model and on the other hand a nonlinear modified associated elastic-perfectly plastic Drucker-Prager model. The different numerical problems were solved within the infinitesimal strains and displacements framework. The finite elements are tetrahedrons (with quadratic basis) which imply more than 2.5 x 10(6) degrees of freedom. The main interest of such a modelling on a large scale, even using a simple constitutive model, is to measure and analyse the evolution of various mechanical fields such as stresses, strains and displacements, during the time evolution of the laboratory. The excavation was performed in 26 steps based on monthly excavation rate performed in situ. The greatest displacements are located in the vicinity of the shaft at the main level of the laboratory, where the cross section is biggest. The areas concerned by shaft-drift or drift-drift intersections are also places of high stress and strain concentration. The area disturbed by the excavation of the shafts is relatively wide. The perturbations induced by the excavation propagated preferentially in a radial direction. However, the zone of extension is relatively restricted such as the plasticity zones. This explains the observation that in the "radial" direction, the influence of the excavation decrease in O(1/r) for the displacement and in O(1/r(2)) for the strain and stress. Thus beyond a given distance, different parts of laboratory work mechanically in a quasi independent manner