Three-dimensional and time stepping modelling of the whore LSMHM-ANDRA laboratory
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 area of the laboratory, a numerical study was performed to model the mechanical behaviour of the whole drifts by using a chronological (time stepping) of the excavations, close to what was realised in reality. Numerical modelling, with considering the geometric scale of the problem, are 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 quadratic tetrahedrons which imply more than two million and half degrees of freedom. The main interest of such a modelling on a large scale, even using simple constitutive model, is to measure and analyse the step-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 at 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 the place 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 zone of extension is relatively restricted such as the plasticity zones. This is why it is observed that beyond a given distance different parts of laboratory work mechanically in a quasi independent manner.In order to understand specific outcome of this type of calculation, comparisons are made in terms of stresses and displacements fields with numerical analysis performed by UPC and DBETEC on a localized mesh with a more complex model which better represent argillite behaviour. Calculations are compared under the niche -445 m around the access shaft and in the specific area formed by GKE, GMR and GEX drifts, which shows important principal stresses rotation which has been confirmed by evidence seen experimentally.