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Macro elements to study the seismic response of shallow and deep foundations

(La Lettre Terrasol, December 2018)

TERRASOL continues to create original computing tools, this time focusing on the development of macro elements to deepen the notion of seismic stability with an estimation of irreversible post-earthquake displacements. The goal is to quantify realistically the inertial efforts transmitted by the upper structure to its foundations. By considering irreversible displacements, even if minimal, it is possible to decrease significantly these efforts compared to calculations that consider a linear elastic behaviour.

In the field of seismic calculations for deep foundations, TERRASOL engaged in a CIFRE PhD work in collaboration with IFSTTAR and ECOLE CENTRALE DE NANTES, in order to develop a macro element capable of estimating the dynamic impedance of a group of piles, accounting for the non-linear effects that characterize the pile / soil / structure interaction. This macro element is being calibrated from numerical modeling as well as physical modeling using a centrifuge.

As for seismic calculations of shallow foundations, we carry out a Research and Development assignment on behalf of EDF-TEGG, aiming to implement in Code_Aster a seismic macro-element which represents the behaviour of an extended shallow foundation (raft type). Simultaneously, we just developed an autonomous computing tool, called FONDSIS, based on an extension of the stick model to the case of a non-linear calculation: the upper structure and the foundation soil are represented by a set of masses, springs and dampers. The soil / structure interface accounts for several combined non-linear mechanisms: bearing capacity, sliding and eccentricity.

S. Burlon and F. Cuira